Surface Alloying and Surface Compositing of Copper Alloys During Casting to Improve Corrosion Resistance, Wear Resistance, and Machinability

Abstract

Disclosed herein are corrosion resistant articles and methods of making the same. The articles include a cast copper alloy component, and a surface modified layer disposed on a surface of the cast copper alloy component, the surface modified layer comprising an surface modifying material selected from the group consisting of Cu, Ni, Cu—Ni, Cu—Sn, Al, Bi, Ni-coated graphite, Ni-coated Al2O3, Ni-coated SiC, uncoated graphite, uncoated SiC, uncoated Al2O3, and any combinations thereof. The methods disclosed herein include providing a slurry having a surface modifying material and a liquid binder. The method further comprises applying the slurry to an insulating tooling (e.g., a core, a mold, or both) to form a slurry-coated tooling, pouring molten copper alloy over the slurry-coated tooling to form a surface modified layer at the interface of the molten copper alloy and the slurry-coated tooling, and solidifying the molten copper alloy and surface modified layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority to U.S. Provisional Patent Application No. 63 / 781,159, filed Mar. 31, 2025, the contents of which are incorporated by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Federal Grant No. 2113857 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD OF THE INVENTION

[0003] The disclosed technology is generally directed to forming surface alloyed and surface composited layers on surfaces during casting. More particularly, the technology is directed forming surface alloyed and surface composited surfaces on copper alloy castings.BACKGROUND OF THE INVENTION

[0004] Brass components are common in water distribution systems; however, brass components are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from harmful metal leaching from the casting into water. The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure.

[0005] Surface alloying is a surface engineering technique that modifies the surface composition of materials to improve specific properties like wear resistance, hardness, and corrosion resistance. While techniques like laser surface alloying, chromizing, and bronzing have been explored, they are expensive and difficult to scale up and are difficult to apply to internal surfaces of components since they require a line of sight and are not universally applicable to copper alloys. Accordingly, a need exists for lower cost, corrosion resistant, leaching resistant, wear resistant, and machinable brass articles and methods of making the same.SUMMARY

[0006] Disclosed herein are lower cost, corrosion resistant, leaching resistant, wear resistant, and machinable brass articles and methods of making the same.

[0007] Disclosed herein is a method of making a copper alloy article, including providing a slurry, applying the slurry to an insulating tooling to form a slurry-coated tooling, contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy, and solidifying the molten copper alloy and surface modified layer. The slurry includes a surface modifying material and a liquid binder. The surface modifying material includes a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof.

[0008] In some cases, the surface modifying material includes Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof, the metal-coated ceramic includes Ni-coated SiC, Ni-coated Al2O3, or any combinations thereof. In some cases, the metal-coated carbon-containing compound includes Ni-coated graphite. The surface modifying material includes particles. In some cases, the surface modifying material comprises particles comprising at least one dimension ranging from about 5 μm to about 300 μm. In certain cases, the surface modifying material includes Cu and Ni and, and the ratio of Cu and Ni is about 1:1.

[0009] In another aspect, the liquid binder comprises water, a polymer, or any combinations thereof. The polymer can include polyvinyl alcohol. In certain embodiments, the liquid binder includes about 0.5 wt % to about 30.0 wt % polymer, based on the total weight of the liquid binder. In some cases, the liquid binder can include a superplasticizer.

[0010] In another aspect, the insulating tooling is a sand mold, a sand core, or any combination thereof. In some cases, the molten copper alloy has a temperature above about 1200° C.

[0011] Another aspect of the methods disclosed herein includes applying the slurry to an insulating tooling and further includes drying the slurry. In some cases, the steps of providing a slurry and applying the slurry to an insulating tooling to form a slurry-coated tooling are repeated two or more times to form a multi-layered slurry-coated tooling.

[0012] Also disclosed herein are corrosion-resistant articles. The articles include a cast copper alloy component and a surface modified layer disposed on a surface of the cast copper alloy component, the surface modified layer comprising a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. In some cases, the cast copper alloy component is includes yellow brass, red brass, bronze, or any combinations thereof.

[0013] In some cases, the surface modified layer Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In certain examples, the surface modified layer is about 1 μm to about 5 mm thick.

[0014] In another aspect of the articles disclosed herein, the corrosion rate of the corrosion resistant article is reduced by 45% to 90%, as compared to the corrosion rate of the cast copper alloy component.

[0015] In another aspect of the articles disclosed herein, the corrosion-resistance article comprises a reduced leach rate of one or more elements into water, as compared to the leach rate of one or more elements into water of the cast copper alloy component.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.

[0017] FIG. 1 shows a schematic of an exemplary embodiment of the methods disclosed herein. Dotted lines indicate optional steps.

[0018] FIG. 2 shows a schematic illustration of the manufacturing process for surface alloyed / surface composited (SASCs).

[0019] FIG. 3 shows scanning electron micrographs of powders used to make the slurry. Panel (a) shows pure Cu powder, panel (b) shows pure Ni powder, panel (c) shows Ni-coated SiC, pane (d) shows Ni-coated Al2O3, panel (e)-(e3) shows elemental image of mounted Ni-Coated SiC particle, and panel (f)-(f3) shows elemental image of mounted Ni-Coated Al2O3 particle.

[0020] FIG. 4 shows optical micrographs of the SASC layer incorporating SiC particles at, in panel (a), low magnifications and, in panel (b), shows high magnifications. The dark regions in panel (a) correspond to Ni-enriched islands formed in situ during solidification. Panel (c) shows area elemental analysis comparing the SASC layer and the base alloy. Panel (d) shows elemental analysis of the phases present within the SASC layer. Panels (e)-(e4) show elemental maps of the SASC layer.

[0021] FIG. 5 shows optical micrographs of the Al2O3-reinforced SASC layer at, in panel (a) low magnifications and, in panel (b), high magnifications. The light regions correspond to Ni-enriched islands formed in situ during solidification. Panel (b) shows highlights the interfacial integrity between the reinforcement particles and the SASC layer. Panel (c) shows area elemental mapping for the SASC sample reinforced with Ni-coated Al2O3 particles, showing a higher Ni content in the SASC layer than in the base alloy. Panel (d) shows elemental analysis of the individual phases present within the SASC layer. (e)-(e4) Elemental maps comparing the SASC layer with the base alloy.

[0022] FIG. 6 shows, in panel (a) and in panel (c), area fraction and average particle size of Ni-rich islands and embedded reinforcements within the SASC layers containing SiC and Al2O3 particles, respectively. Panels (b) and (d) show area fraction and average particle size of Bi precipitates in the corresponding SASC layers, respectively.

[0023] FIG. 7 shows, in panel (a) and in panel (b), SASC layer thickness and surface coverage measured in the cast SASCs, respectively. Panel (c) and panel (d) show Ni-depleted zone length and Ni shell thickness in the cast SASCs, respectively.

[0024] FIG. 8 shows corrosion current results from the Potentiodynamic cell test.

[0025] FIG. 9 shows microhardness results of the S0 base alloy and SASC sample.

[0026] FIG. 10 shows an X-ray diffraction (XRD) plot of the Al2O3 and SiC SASCs.

[0027] FIG. 11 shows adhesion test results of the SASC samples with Ni—Al2O3 (S1) and Ni—SiC (S3) before heating (in panel a1 and panel b1), after heating to 250° C. (panel a2 and panel b2), and after heating to 400° C. (panel a3 and panel b3) and rapidly cooling by water quenching to room temperature. There is no delamination of the SASC layer.

[0028] FIG. 12 shows machinability test showing the formation of chips from the surface machining of, in panel (a), yellow brass, in panel (b), base alloy C89836, in panel (c), base alloy with surface alloyed layer and, in panel (d) base alloy with SASC layer containing Al2O3 particles. The image in panel (d) shows much smaller chips.

[0029] FIG. 13 shows, in panel (a) an electron micrograph and associated elemental analysis of the individual phases present within the SASC layer (Spectrum 1) and the base copper alloy (Spectrum 2). Panel (b) shows corrosion rate of the surface alloyed casting as compared to un-modified red brass and yellow brass. Panel (c) shows a picture of a cross section of a sample, with the surface alloyed layer circled.

[0030] FIG. 14 panel (a) shows optical microstructure of cross-section of casting showing the surface alloyed (SA) layer and base metal shows some porosity) in panel (b) shows SEM / EDS data showing the elemental gradients of Ni, Cu, Zn, and Sn from the SA layer toward the substrate Bi-Alloy, including enrichment of Nickel in the surface alloyed layer. Panel (c), and panel (d) show SEM / EDS data showing the elemental gradient of Zn and Cu within the SA layer and substrate yellow brass, including higher copper content in the SA layer compared to the base alloy.

[0031] FIG. 15 panel (a) shows yellow brass castings made at RheoCast Foundry using the surface alloying process on coated molds, panel (b) shows molds and cores used to cast internally surface alloyed Bi-Alloy castings, panel (c) shows water industry casting made using bi-alloy and coated cores.

[0032] FIG. 16 shows the highest thickness of surface alloyed layer alongside the sample numbers corresponding to samples described in Table 8.

[0033] FIG. 17 shows optical microscope images of samples described in Table 8. All scale bars are 500 μm.

[0034] FIG. 19 shows an electron micrograph and corresponding EDS map of Si and Ni elements from a portion of the surface alloyed layer of sample 47.

[0035] FIG. 18 shows Ni—Cu phase diagram.

[0036] FIG. 20 panel (a) shows final casting of sample S9 of Table 16 showing the surface alloyed layer, panel (b) shows metallographically prepared sample etched with Copper No 2 etchant showing the Ni enriched layer, panel (c) shows microstructural image of the sample S9 showing the surface alloyed layer and base metal.

[0037] FIG. 21 shows an optical micrograph of sample S9 of Table 16, showing SA layer with an average thickness of 1.2 mm.

[0038] FIG. 22 shows an electron micrograph of Sample S9, showing elemental analysis maps by EDS for Cu, Ni, Sn, C, and Zn. Elemental composition is also given as a function of distance for a line trace crossing from the SA layer to the bulk metal is indicated on the electron micrograph.

[0039] FIG. 23 shows an electron micrograph of Sample S18, showing elemental analysis by EDS for Cu, Ni, Sn, C, and Zn. Elemental composition is given as a function of distance for a line trace crossing from the SA layer to the bulk metal is indicated on the electron micrograph.

[0040] FIG. 24 shows an electron micrograph of Sample S27 of Table 16, with inset indicating locations where elemental analysis was performed for Al, Cu, and Zn and shown in Table 23.

[0041] FIG. 25 shows in panels (a) and (c), cores from industry partner coated with metal powder slurry, and in panel (b) an as-cast surface alloyed component.

[0042] FIG. 26 shows polarized optical micrographs showing the microstructure of the surface-alloyed and surface composited layer (using PVA binder) formed on C89836 brass casting. The images show distinct surface-alloyed and surface composited layers composed of blue Ni-rich regions (islands), dark graphite particles and multiphase microstructure. Panel (a) and panel (b) show low magnification image from the SASC layer. Panel (c) and panel (d) show regions between Ni-rich islands containing graphite particles. Panel (e) and panel (f) high magnification view of the Ni-rich regions (islands) occasionally containing Bi-rich phase within them, and graphite particles around the Ni-rich regions.

[0043] FIG. 27 shows, in panel (a), the average thickness of three types formed of surface layers on C89836 brass substrate during the casting process. Panel (b) shows the average surface coverage observed in the three types of surface layers on C89836 brass castings using different slurry compositions.

[0044] FIG. 28 shows the area percentage of graphite particles within the SASC layer formed on C89836 brass castings with PVA and with PVA+Superplasticizer used as the binders.

[0045] FIG. 29 shows the distribution and morphology of nickel-rich islands within the three surface alloy layer types formed on C89836 brass castings. Panel (a) shows the area percentage, while panel (b) shows the average size of the Ni-rich islands.

[0046] FIG. 30 shows SASC sample with incorporation of Ni-coated Graphite powder in the slurry showing formation of Ni-rich islands and incorporated graphite particles in the SASC layer. (Sample 2)

[0047] FIG. 31 shows elemental mapping showing the presence of Ni, Cu, Zn and graphite in the SASC layer. Enrichment in Ni is observed around the graphite particles.

[0048] FIG. 32 shows SASC sample with Ni-Graphite showing formation of Ni-rich islands in the SASC layer (Sample 1), which are surrounded by graphite particles.

[0049] FIG. 33 shows elemental mapping showing the presence of Ni, Cu, and Zn in the SASC layer. Ni distribution is visible around the graphite particles.

[0050] FIG. 34 show line scans showing an increase in Ni (bottom right) and Cu (bottom left) along the surface of graphite particles, incorporated in the SASC layer.

[0051] FIG. 35 shows XRD mapping of the SASC sample showing the presence of graphite and Cu—Ni phase.

[0052] FIG. 36 shows a comparison of Icorr for yellow brass, C89836, and the SA and SASC samples showing an increase in corrosion resistance on account of surface modification.

[0053] FIG. 37 shows a comparison of lead concentration in water in ppb, for base alloy, SASC sample, and the water control samples.

[0054] FIG. 38 shows comparison of chips collected during machining of three different brass-based samples, produced by sweeping a drill bit across the surface of each material at a cutting depth of 10 in / 1000. Optical and SEM images of chips formed during machining tests of the 60-40 alloy (panels a and a1), the C89836 alloy (panels b and b1), the Ni—Cu SA layer (panels c and c1), and the Ni-Graphite SASC layer (panels d and d1). Panels (e and e1) present higher-magnification SEM images of the chips in (d1), with corresponding carbon mapping, showing graphite particles embedded in the SASC layer. The dashed circles indicate carbon-enriched regions, indicating how the embedded graphite particles promote breaking of chips and thereby enhances the machinability of the SASC samples.DETAILED DESCRIPTION OF THE INVENTION

[0055] Disclosed herein are corrosion resistant, wear resistant, and / or leaching resistant articles and methods of making the same. More specifically, disclosed herein are corrosion resistant copper alloy (e.g., brass such as yellow brass or red brass, bronze alloys, and other copper alloys) articles and methods of making the same. As used herein, the terms “copper alloy” and “brass” and “bronze” are used synonymously. The present disclosure describes a low-cost surface alloying and / or surface compositing method that enriches the surface of a brass casting with selected materials that increase corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance, and / or that incorporate particles including graphite, silicon carbide, and / or alumina on the surface of castings to impart wear resistance and machinability.

[0056] In some examples, the methods disclosed herein include a step of applying a slurry to tooling to form a slurry-coated tooling. As used herein, “casting tooling” or “foundry tooling” or “tooling” refers to the engineered components used to create the geometry of a casting, including molds and cores. As used herein, the term “tooling” refers to molds, cores, and combinations thereof. In some cases, tooling may be made from sand, metal, ceramic, graphite, or other refractory materials.Methods

[0057] Referring to FIG. 1, disclosed herein is a method of making a copper alloy article (1). The method includes providing a slurry (100) including a surface modifying material and a liquid binder. The surface modifying material can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. The method further includes applying the slurry to an insulating tooling to form a slurry-coated tooling (200). The method further includes contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy, (300) and solidifying the molten copper alloy and surface modified layer.

[0058] In some examples, the method disclosed herein includes providing a slurry including a surface modifying material and a liquid binder. As used herein, a “slurry” refers to a mixture of solid particles dispersed in a liquid. The slurry includes at least one surface modifying material. As used herein, the term “surface modifying material” refers to a material present on the surface of tooling and interacting with hot, molten copper alloy, creating a modified layer on at least one surface of a copper alloy casted component. The resulting surface modified layer is formed between the bulk of the copper alloy and the tooling, and resides on the surface of the cast component produced as result of the methods disclosed herein.

[0059] In some cases, the surface modified layer is a surface alloyed layer, a surface composited layer, or a combination thereof. As used herein, “surface modified layer” refers to a surface-confined modification of a component having a bulk metallic component, such as copper alloy like brass or bronze. As used herein, “surface alloying” refers to the process where the molten copper alloy interacts with a metallic surface modifying material on a surface of tooling to produce a surface region which is enriched in metallic alloying elements (e.g., Cu, Ni, Bi, Sn, etc.). This enriched region may, for example, enhance corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance. In some cases, interacting refers to melting. In some cases, interacting at the surface refers to dissolution. As used herein, “surface compositing” refers to the process where non-metallic surface modifying components (e.g, uncoated graphite, uncoated SiC, uncoated Al2O3, metal-coated graphite, metal-coated Al2O3, metal-coated SiC, other solid lubricants and ceramic particles, and any combinations thereof) are incorporated in the surface region of the castings of copper alloys. In some cases, non-metallic surface modifying components are transferred from the slurry to the molten copper alloy to form a surface composite on the resulting copper alloy article. In some cases, non-metallic surface modifying components are transferred from the slurry-coated tooling to the surface of the cast copper alloys to form a surface composite on a surface of a resulting copper alloy article

[0060] Surface modifying materials can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. In some cases, the surface modifying material may include one or more metals. More specifically, the surface modifying material may include Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In some cases, the metal-coated alloying materials may be coated with nickel or copper (e.g., Ni-coated graphite, Ni-coated Al2O3, Ni-coated SiC, Cu-coated graphite, Cu-coated Al2O3, Cu-coated SiC).

[0061] In some cases, the surface modifying material includes an alloying element. In some cases, the alloying element includes a metal. Examples of metal may include Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Al, Ga, In, Sn, Tl, Pb, Bi, Po, or any combinations thereof.

[0062] In some cases, the surface modifying materials include a metallic alloy. Examples of metallic alloy may include Cu—Sn, Cu—Zn, Cu—Ni, Cu—Al, Cu—Be, Cu—Si, Cu—Mn, Cu—P, Ni—Cr, Ni—Fe, Ni—Mo, Ni—Cu, Ni—Co, Ni—Ti, Fe—C, Fe—Cr, Fe—Cr—Ni, Fe—Mn, Fe—Si, Fe—Ni, Fe—Mo, Fe—W, Al—Si, Al—Mg, Al—Cu, Al—Zn, Al—Mn, Al—Li, Mg—Al, Mg—Zn, Mg—Mn, Mg—Y, Mg—Gd, Ti—Al, Ti—V—Al, Ti—Nb, Ti—Mo, Co—Cr, Co—Cr—Mo, Zn—Al, Zn—Cu, Zn—Mg, or any combinations thereof.

[0063] In some cases, the surface modifying materials include a carbon-containing compound. Examples of carbon-containing compounds include diamond, graphite, amorphous carbon, lonsdaleite (hexagonal diamond), fullerenes (c60, c70, etc.), carbon nanotubes (single-walled, multi-walled), graphene, graphene oxide, reduced graphene oxide, activated carbon, glassy carbon, carbon black, soot, charcoal, coke (petroleum coke, metallurgical coke), nanofoam carbon, carbon aerogel, q-carbon, carbyne, amorphous diamond (tetrahedral amorphous carbon), turbostratic carbon, or any combinations thereof. In some cases, the carbon-containing compound may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0064] In some cases, the surface modifying materials include a ceramic. In some cases, the ceramic includes oxides (e.g., Al2O3, ZrO2, SiO2, MgO, CaO, HfO2, ThO2, BeO, ZnO, TiO2, Cr2O3, spinels, perovskites, mullite, cordierite, zircon, magnesium silicates), carbides (e.g.SiC, WC, B4C, TiC, TaC, NbC, VC, HfC, Cr3C2), nitrides (e.g., Si3N4, AlN, BN, TiN, ZrN, HfN, CrN), oxynitrides (e.g., SiAlON, AlON), borides (e.g., TiB2, ZrB2, HfB2, CrB2), silicides (e.g., MoSi2, WSi2, TiSi2, CrSi2), refractory silicates & phyllosilicates (e.g., Al2Si2O5(OH)4, Mg3Si4O10(OH)2, Al2Si4O10(OH)2, montmorillonite / bentonite clays), and any combinations thereof. The incorporation of ceramic particles may improve the wear resistance of castings and reduce the leaching of harmful elements in water. In some cases, the ceramic particles may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0065] In some cases, the surface modifying material includes a solid lubricating material. Examples of solid lubricating materials include graphite, molybdenum disulfide, tungsten disulfide, hexagonal boron nitride (h-BN), Pb, Sn, Ni, In, bismuth oxide, copper oxide, silicon nitride, silver-based lubricating phases, barium fluoride, calcium fluoride, or any combinations thereof.

[0066] In some cases, the surface modifying material is a powder. In some cases, the powder includes particles. In some cases, the particles have at least one dimension ranging from about 1 μm to about 1000 μm, from about 3 μm to about 500 μm, from about 5 μm to about 300 μm, or from about 10 μm to about 250 μm. In some cases, the Ni particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 50 μm to about 175 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Al particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Cu particles have at least one dimension ranging from about from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Bi particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 10 μm to about 170 μm, from about 8 μm to about 200 μm, from about 10 μm to about 200 μm, or from about 5 μm to about 215 μm. In some cases, the Cu—Sn particles have a particles size ranging from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the metal-coated Al2O3 particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 25 μm to about 275 μm, from about 10 μm to about 300 μm, from about 15 μm to about 275 μm, or from about 50 μm to about 250 μm. In some cases, the metal-coated graphite particles have at least one dimension ranging from about 16 μm to about 200 μm, from about 5 μm to about 500 μm, from about 25 μm to about 275 μm, from about 10 μm to about 300 μm, from about 15 μm to about 275 μm, or from about 50 μm to about 250 μm. In some cases, the metal-coated SiC particles have at least one dimension ranging from about 10 μm to about 100 μm, from about 5 μm to about 500 μm, from about 50 μm to about 175 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. There are several suitable methods and standards for determining particle size, including ASTM E11, ASTM B822, ASTM E112, and ASTM E2651. For example, according to ASTM B822, particle size distribution can be determined using laser diffraction based on Fraunhofer diffraction, Mie scattering, or a combination of both. The scattering data are analyzed by assuming a spherical particle model; therefore, the reported particle size is expressed as an equivalent spherical diameter. In other words, the particle size corresponds to the diameter of a sphere having the same scattering characteristics (or projected area) as the actual particle.

[0067] In some cases, the surface modifying material includes a combination of Ni particles, Cu particles, and at least one non-metallic particle. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0068] In some cases, the surface modifying material includes Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al. In some cases, the ratio of Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al is about 1:1. In some cases, the ratio of Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al is about 100:1, about 50:1, about 25:1, about 10:1, about 9:1, about 5:1, about 4:1, about 3:1, about 2:1, about 1:1, about 1:2, about 1:3, about 1:4, about 1:5, about 1:9, about 1:10, about 1:25, about 1:50, or about 1:100.

[0069] In some cases, the surface modifying material includes at least one pair selected from Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al. For example, if Ni and Cu metals are selected, the surface modifying material may include a powder mixture of Ni particles and Cu particles. In another example, in the case where Cu and Sn are selected, the surface modifying material may include an alloy powder of Cu—Sn particles. For example, the alloy powder of Cu—Sn may be a a 90-10 alloy of Cu—Sn. The surface modifying material further includes at least one non-metallic particle. In some cases, the surface modifying material includes Cu and Ni and at least one non-metallic particle. In some cases, the ratio of Cu to Ni to the at least one metal-coated non-metallic particle is about 1:1:0.1, about 1:1:0.2, about 1:1:0.3, about 1:1:0.4, about 1:1:0.5, about 1:1:0.6, about 1:1:0.7, about 1:1:0.8, about 1:1:0.9, about 1:1:1.

[0070] In some cases, the slurry includes about 1:1:0.6 ratio of Cu, Ni, and metal-coated non-metallic particle and about 10 wt % polymer in a solvent, based on the total weight of the polymer and solvent. In some cases, the metal-coated non-metallic particle includes Ni-coated Al2O3, Ni-coated SiC powders, or a combination thereof. In some cases, the slurry further includes a superplasticizer.

[0071] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Ni, based on the total weight of the surface modifying materials in the slurry.

[0072] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Cu, based on the total weight of the surface modifying materials in the slurry.

[0073] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 20 wt % to about 30 wt %, about 22 wt % to about 28 wt %, or about 23 wt % to about 26 wt % of a non-metallic particle, based on the total weight of the surface modifying materials in the slurry. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0074] In some instances, the slurry may include about 0.1 wt % to about 50 wt %, about 1.0 wt % to about 30 wt %, about 0.1 wt % to about 8.0 wt %, about 0.2 wt % to about 10 wt %, about 0.3 wt % to about 10 wt %, about 0.5 wt % to about 5.0 wt %, or about 1.0 wt % to about 4.0 wt % of bismuth, based on the total weight of the surface modifying materials in the slurry.

[0075] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Sn, based on the total weight of the surface modifying materials in the slurry.

[0076] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Al, based on the total weight of the surface modifying materials in the slurry.

[0077] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Ni—Cu, based on the total weight of the surface modifying materials in the slurry.

[0078] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Cu—Sn, based on the total weight of the surface modifying materials in the slurry.

[0079] Referring to Example 1, the slurry can include about 38 wt % Cu, about 38 wt % Ni, and about 24 wt % of a non-metallic component. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0080] In another aspect of the methods disclosed herein, the slurry includes a liquid binder. The liquid binder may include water, a polymer, or any combination thereof. In some cases, the liquid binder includes about 0.5 wt % to about 50 wt %, about 0.5 wt % to about 40 wt %, about 1.0 wt % to about 30 wt %, about 2.0 wt % to about 25 wt %, about 3.0 wt % to about 20 wt %, about 4.0 wt % to about 10 wt %, about 4.0 wt % to about 15 wt %, polymer, based on the total weight of the liquid binder. In some cases, the polymer includes polyvinyl alcohol (PVA) or sodium polyacrylate. As shown in the below Examples, other binders which disperse the surface modifying material can be used, such as modified commercial mold and core coatings. For example, modified Refcobar 1010 gel (a water-based core and mold coating with refractory material omitted) or modified Vibrantz binder (a water-based core and mold coating with refractory material omitted) may be used. In some cases, the liquid binder further includes a superplasticizer which leads to increased dispersion and fluidity in the slurry. In some cases, the superplasticizer includes a polycarboxylate superplasticizer (e.g., MEGAPOL GUSR-AC).

[0081] In another aspect, there is a ratio of polymer to surface modifying material in the liquid binder. The ratio of polymer to surface modifying material may be selected based on the viscosity of the resulting slurry. For example, a liquid binder having 4 wt % polymer will have low viscosity and thus, will be added in a lower quantity to act as the binder. Similarly, a liquid binder having 10 wt % polymer solution, due to its higher viscosity, may be added in a slightly higher amount. In some cases, the ratio of surface modifying material to polymer in the liquid binder may include about 40 wt % of surface modifying material to about 10 wt % polymer. For example, approximately 5 grams of 10 wt % polymer was added 13.168 grams of surface modifying material. In some cases, up to about 45 wt % of the surface modifying material to about 10 wt % polymer may be used.

[0082] The methods disclosed herein include a step of applying the slurry to tooling to form a slurry-coated tooling. As used herein, “casting tooling” or “foundry tooling” or “tooling” refers to the engineered components used to create the geometry of a casting, including molds and cores. As used herein, the term “tooling” is used to refer to molds, cores, and other components for casting . . . . In some cases, tooling may be made from sand, metal, ceramic, graphite, or other refractory materials. In some cases, the tooling may include low-thermal conductivity materials (i.e., thermally insulating materials). These “insulating tooling” are intended to absorb heat slowly, minimize thermal shock, and / or control local solidification in the surrounding, cooling molten copper alloy and / or surface modified layer. In some cases, the insulating tooling comprises sand, for example sand mold or a sand core. As used herein, the term “mold” refers to a cavity (e.g., a mold) defining negative space that forms at least one external or internal surface of a cast component. For example, a mold is a shaped cavity into which molten metal is poured to solidify into a desired geometry. The mold provides the negative imprint of the final component. As used herein, the term “core” refers to a shaped insert placed inside a mold to create internal surfaces, hollow sections, or complex internal geometries in a casting. In some cases, where the tooling includes a mold and a core, in addition to or alternative to applying the slurry to a mold (e.g., a sand mold), the slurry is applied to a core (e.g., a sand core) used with a mold, and then the slurry-coated core (and / or mold) is contacted with the molten copper alloy to interact with the slurry to form the surface modified layer. Applying the slurry to tooling to form a slurry-coated tooling may include any suitable method for coating a surface with a liquid mixture, such as painting, brushing, dipping, spraying, flowing, troweling, daubing, or dip-spinning.

[0083] Referring still to FIG. 1, the method may further include drying the slurry-coated tooling (201) before contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy (300). Drying times for the slurry may vary depending upon a thickness of the applied slurry. In some cases, the slurry-coated tooling may be dried for at least about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 19 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, about 25 hours, about 26 hours, about 27 hours, about 28 hours, about 29 hours, about 30 hours, about 31 hours, about 32 hours, about 33 hours, about 34 hours, about 35 hours, about 36 hours, about 37 hours, about 38 hours, about 39 hours, about 40 hours, about 41 hours, about 42 hours, about 43 hours, about 44 hours, about 45 hours, about 46 hours, about 47 hours, about 48 hours, about 49 hours, about 50 hours, about 51 hours, about 52 hours, about 53 hours, about 54 hours, about 55 hours, about 56 hours, about 57 hours, about 58 hours, about 59 hours, about 60 hours, about 61 hours, about 62 hours, about 63 hours, about 64 hours, about 65 hours, about 66 hours, about 67 hours, about 68 hours, about 69 hours, about 70 hours, about 71 hours, about 72 hours, or more. The slurry-coated tooling may be dried by methods such as air drying or low-temperature furnace drying. The slurry-coated tooling may be dried at room temperature, temperatures above room temperature, or temperatures below room temperature.

[0084] In some cases, still referring to FIG. 1, the steps of providing a slurry (100) and applying the slurry to an insulating tooling to form a slurry-coated tooling (200) may be repeated (400) multiple times to form a multi-layered slurry-coated tooling. In some cases, the step of drying the slurry-coated tooling (201) may be repeated (500). In some cases, the slurries used in subsequent repeats of steps (100) and (200) are substantially compositionally the same as earlier-applied slurries. In some cases, the slurries used in subsequent repeats of steps (100) and (200) are substantially compositionally different than earlier-applied slurries.

[0085] The methods disclosed herein further include contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy. Contacting the slurry-coated tooling with molten copper alloy includes any suitable method for introducing a liquid metal to a tooling, such as pouring, ladling, pressure-assisted filling (e.g., gas-pressurized filling, low-pressure casting), gravity sand casting, injection, centrifugal casting, vacuum-assisted pouring (e.g., counter-gravity casting), or squeeze casting. In some cases, the method further includes pouring the molten copper alloy in the slurry-coated tooling to synthesize a surface modified layer on the cooper alloy casting upon the completion of solidification of the molten copper alloy. The method further includes pouring the molten copper into the mold and the slurry-coated core forms a surface modified layer through interfacial interaction during the solidification of the molten copper alloy.

[0086] Contacting the slurry-coated tooling with molten copper alloy includes heating the copper-based alloy (e.g., to a temperature above the melting point of the copper alloy, such as a temperature above 1200° C., or a temperature between about 1200° C. to about 1300° C., or to a temperature higher than 1300° C., described further elsewhere herein) and pouring the molten copper-based alloy into the (coated) tooling. As a result, at least part of the applied slurry may interact with the molten copper-based alloy at the surface to form the surface modified layer on the surface of the casting. The surface modified layer is disposed between the slurry-coated insulating tooling and the bulk copper alloy. In some cases, heating the molten copper alloy to a temperature exceeding its melting temperature (i.e., a superheat) before it is poured into the slurry-coated tooling may be desirable. As used herein, “superheat” refers to the amount by which the temperature of the molten copper alloy exceeds its melting temperature before it is poured into a mold. For example, if a brass alloy has a melting temperature of 930° C. and it is poured into a mold at a temperature of 1030° C., the superheat is 100° C. In some cases, a superheat of about 50° C., about 100° C., about 150° C., about 200° C., about 250° C., about 300° C., about 350° C., about 400° C., about 450° C., or about 500° C. may be used in the methods disclosed herein. In some cases, contacting the slurry-coated tooling with molten copper alloy (300) may include heating the tooling in advance of pouring the molten copper-based alloy into the (coated, heated) tooling. In some cases, the tooling may be heated to about 30° C., about 40° C., about 50° C., to about 75° C., to about 100° C., to about 125° C., to about 150° C., to about 175° C., to about 200° C., to about 225° C., to about 250° C., to about 275° C., to about 300° C., or higher. Superheat may affect the thickness of the resulting surface modified layer.

[0087] When the slurry-coated tooling comes in contact with molten copper alloy it may cause a phase change (e.g., melting) of one or more of the components of the slurry. In some cases, contact between the slurry-coated tooling and molten copper alloy followed by melting and / or dissolution of metal powder in the slurry. In some cases, contacting the slurry-coated tooling and molten copper alloy is followed by dissolution and / or mixing and diffusion of one or more of the components of the slurry into the molten copper alloy. In some cases, the dissolution and / or mixing and diffusion is confined to less than about 10 mm, about 9 mm, about 8 mm, about 7 mm, about 6 mm, about 5 mm, about 4 mm, about 3 mm, about 2 mm, about 1 mm, about 0.5 mm, about 0.2 mm, about 0.1 mm, or about 0.05 mm from the surface of the resulting copper alloy article. In some cases, the contact between the slurry-coated tooling with molten copper alloy forms a composite. Forming a composite may result from the interaction of the heat of the molten copper alloy with the components of the slurry to transform (e.g., by melting, by dissolution). In some cases, a metal component of the slurry may melt or dissolve, mix and diffuse. In some cases, when the slurry contains a nickel-coated component (e.g., Ni-coated graphite, Ni-coated SiC, Ni-coated Al2O3), the nickel coating may dissolve. In some cases, forming a composite may include transferring ceramic particles in the slurry coating to a surface layer of the resulting copper alloy article, forming a surface composited layer.

[0088] The methods disclosed herein further include solidifying the molten copper alloy and surface modified layer. Forming the surface modified layer can include solidifying the copper-based alloy. Solidifying the copper-based alloy includes cooling the molten copper-based alloy to a temperature below the melting point of the copper-based alloy. In some cases, solidifying the copper-based alloy includes cooling the copper-based alloy to a temperature below about 1300° C., below about 1200° C., or below about 1000° C. Cooling the molten copper-based alloy may include removing a source of heat. Cooling may include conduction, convection, or radiation of heat from the copper-based alloy and / or tooling. These mechanisms of heat extraction may occur concurrently for the cooling of the molten copper-based alloy.

[0089] The advantages of the surface alloyed layer are multifold. In some cases, the properties of the surface alloyed layer are tailorable based upon the composition, viscosity, preheating, and thickness of the slurry layer or layers applied to the tooling, the melt temperature of the molten brass, and the tooling temperature. More specifically, the properties of the surface alloyed / surface composited (SASC) layers depend on the metallic alloying materials (e.g., Cu, Ni, Bi, Sn, etc), type of ceramic or non-metallic particles (e.g., SiC, Al2O3, graphite, etc), and the ratio in which the metallic alloying materials and non-metallic or ceramic particles are mixed or the thickness of the slurry that is applied on the tooling. In some cases, the viscosity of the slurry is important for the application of the slurry to a surface, but the primary effect on the surface alloyed layer's properties is driven by the materials present in the surface alloyed layer. In some cases, the surface alloyed layer improves the corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance and machinability of the brass component while eliminating or reducing the need for lead or bismuth in the alloy and maintaining machinability. The enrichment of surface of the castings with a surface alloyed layer may also reduce the leaching of undesirable or harmful elements in contact with water. The incorporation of graphite on surfaces of brass castings can impart machinability to castings without use of lead or bismuth additions and can reduce corrosion and leaching of undesirable or harmful elements in water.

[0090] The methods disclosed herein can reduce costs compared to conventional methods for creating surface alloyed / surface composited layers, such as thermal spray, electroplating, laser surface alloying, or vacuum-based coating (e.g., vacuum deposition), by maintaining compatibility with existing casting techniques. Furthermore, because only the surface may be enriched, the bulk copper alloy composition remains largely unchanged, thus preserving the beneficial properties of brass while enhancing its corrosion resistance, leaching resistance, wear resistance, oxidation resistance, and / or machinability at critical surface regions. The surface alloyed / surface composited castings of this work conserve expensive alloying elements, like nickel, copper, and bismuth, to surface layers because, at least in some examples, they are incorporated only near the surface in comparison to through section full thickness. In comparison to full-thickness alloyed castings, where the expensive alloying elements are present all through the cross section, the methods described herein can offer significant reduction in alloying elements, resulting in cost savings.Articles

[0091] Disclosed herein are corrosion-resistant, oxidation resistant, wear resistant, and leaching resistant articles including a cast copper alloy component and a surface modified layer disposed on a surface of the cast copper alloy component. In some cases, the cast copper alloy component includes yellow brass, red brass, bronze, or any combinations thereof.

[0092] The articles disclosed herein define an interior surface and an exterior surface. In some instances, the interior surface defines a cavity or a passageway through the article. In some cases, the interior surface and the exterior surface each include the surface modified layer. In some cases, the interior surface includes the surface modified layer. In other cases, the exterior surface includes the surface modified layer.

[0093] The articles disclosed herein may include articles cast from a copper-based alloy. For example, the article may include a valve or other flow-control components (e.g., butterfly valve, check valve, ball valve, gate valve, globe valve, pressure-reducing valve, backflow preventer, foot valve, solenoid valve body, diverter valve, tubes or pipes), plumbing, piping, and / or pumping components (e.g, fitting (e.g., a pipe fitting), elbow, tee, coupling, union, adapter, hose bibb, faucet body, faucet cartridge, mixing valve body, manifold block, water meter body, pump impeller, pump housing, suction diffuser, basket strainer, Y-strainer), HVAC and / or refrigeration components (e.g., a refrigeration valve body, expansion valve body, compressor fitting), marine hardware (e.g., propeller hubs, sea strainer, pump housings, thru-hull fitting, marine pump component, deck hardware, or propeller hub), industrial and instrumentation components (e.g., pressure gauge housing, flowmeter body, electric connector housing, cable-gland body, switch housing, fuse block), fire protection components (e.g., sprinkler head, sprinkler valve body, fire nozzle body), mechanical hardware (e.g., gear (low-stress), bushing, bearing shell, hinge component, lock body, door hardware), or decorative or architectural articles (e.g., door handle, door knob, door pull, lighting fixture, lamp base, ornamental casting, clock component).

[0094] In some cases, the surface modified layer is a surface alloyed layer, a surface composited layer, or a combination thereof. The surface modified layer can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. More specifically, the surface modified layer may include Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In some cases, the metal-coated materials may be coated with nickel or copper (e.g., Ni-coated graphite, Ni-coated Al2O3, Ni-coated SiC, Cu-coated graphite, Cu-coated Al2O3, Cu-coated SiC).

[0095] In some cases, the surface modified layer includes a metal. Examples of metals may include Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Al, Ga, In, Sn, Tl, Pb, Bi, Po, or any combinations thereof.

[0096] In some cases, the surface modified layer includes a metallic alloy. Examples of metallic alloys may include Cu—Sn, Cu—Zn, Cu—Ni, Cu—Al, Cu—Be, Cu—Si, Cu—Mn, Cu—P, Ni—Cr, Ni—Fe, Ni—Mo, Ni—Cu, Ni—Co, Ni—Ti, Fe—C, Fe—Cr, Fe—Cr—Ni, Fe—Mn, Fe—Si, Fe—Ni, Fe—Mo, Fe—W, Al—Si, Al—Mg, Al—Cu, Al—Zn, Al—Mn, Al—Li, Mg—Al, Mg—Zn, Mg—Mn, Mg—Y, Mg—Gd, Ti—Al, Ti—V—Al, Ti—Nb, Ti—Mo, Co—Cr, Co—Cr—Mo, Zn—Al, Zn—Cu, Zn—Mg, or any combinations thereof.

[0097] In some cases, the surface modified layer includes a carbon-containing compound. Examples of carbon-containing compounds include diamond, graphite, amorphous carbon, lonsdaleite (hexagonal diamond), fullerenes (c60, c70, etc.), carbon nanotubes (single-walled, multi-walled), graphene, graphene oxide, reduced graphene oxide, activated carbon, glassy carbon, carbon black, soot, charcoal, coke (petroleum coke, metallurgical coke), nanofoam carbon, q-carbon, carbyne, amorphous diamond (tetrahedral amorphous carbon), turbostratic carbon, or any combinations thereof. In some cases, the carbon-containing compound may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0098] In some cases, the surface modified layer includes a ceramic. In some cases, the ceramic includes oxides (e.g., Al2O3, ZrO2, SiO2, MgO, CaO, HfO2, ThO2, BeO, ZnO, TiO2, Cr2O3, spinels, perovskites, mullite, cordierite, zircon, magnesium silicates), carbides (e.g. SiC, WC, B4C, TiC, TaC, NbC, VC, HfC, Cr3C2), nitrides (e.g., Si3N4, AlN, BN, TiN, ZrN, HAN, CrN), oxynitrides (e.g., SiAlON, AlON), borides (e.g., TiB2, ZrB2, HfB2, CrB2), silicides (e.g., MoSi2, WSi2, TiSi2, CrSi2), refractory silicates & phyllosilicates (e.g., Al2Si2O5(OH)4, Mg3Si4O10(OH)2, Al2Si4O10(OH)2, montmorillonite / bentonite clays), and any combinations thereof.

[0099] In some cases, the surface modified layer includes a solid lubricating material. Examples of solid lubricating materials include graphite, molybdenum disulfide, tungsten disulfide, hexagonal boron nitride (h-BN), Pb, Sn, Ni, In, lead oxide, bismuth oxide, copper oxide, silicon nitride, silver-based lubricating phases, barium fluoride, calcium fluoride, or any combinations thereof.

[0100] In some cases, the transition between the surface modified layer of an article and the bulk material of the article is a sharp interface (i.e., there is a clear boundary between the surface modified layer and the underlying bulk metal). In other cases, the transition between the surface modified layer of an article and the bulk material of the article is gradual (i.e., there is no clear delineation between the surface modified layer and the underlying bulk metal).

[0101] In another aspect, the surface modified layer has a thickness, as measured from the surface of the copper alloy article. In some cases, the thickness ranges from about 1 μm to about 5 mm, from about 0.1 μm to about 5 mm, from about 1 μm to about 5 mm, from about 1 μm to about 2000 μm, from about 200 μm to about 1500 μm, or from about 350 μm to about 1500 μm. In some cases, the surface modified layer may have a thickness of about 10 nm to about 10,000 μm. In various instances, surface modified layers may have a thickness of about 100 nm to about 10,000 μm. In various instances, surface modified layers may have a thickness of about 1 μm to 10,000 μm; 25 μm to 5,000 μm; 50 μm to 2,500 μm; or 100 μm to 1,000 μm. In various instances, surface modified layers may have a thickness of no greater than 10,000 μm; no greater than 9,000 μm; no greater than 8,000 μm; no greater than 7,000 μm; no greater than 6,000 μm; no greater than 5,000 μm; no greater than 4,000 μm; no greater than 3,000 μm; no greater than 2,000 μm; or no greater than 1,000 μm. In various instances, surface modified layers may have a thickness of no less than 10 nm; no less than 100 nm; no less than 1 μm; no less than 10 μm; no less than 20 μm; no less than 30 μm; no less than 40 μm; no less than 50 μm; no less than 60 μm; no less than 70 μm; no less than 80 μm; no less than 90 μm; or no less than 100 μm.

[0102] The composition of the surface modified layer of the articles disclosed herein varies with the composition of the slurry containing surface modifying materials used in manufacturing the articles. It may also depend on the composition of the base copper-based alloy used to form the bulk of the article. Tables 4-7 in Example 1 offer exemplary compositions of the surface modified layer as well as the underlying base (a copper based alloy).

[0103] In some cases, the surface modified layer includes oxygen, aluminum, nickel, copper, zinc, tin, bismuth, silicon, and any combinations thereof. Other elements may also be present in the surface modified layer. The surface modified layer may include elements present in the surface modifying material. For example, in cases where the surface modifying material includes Al2O3, the surface modified layer may include aluminum and oxygen. The surface modified layer may include about 6 wt % to about 12 wt % oxygen. The surface modified layer may include about 0 wt % to about 20 wt % aluminum, or about 12 wt % to about 20 wt % aluminum. The surface modified layer may include about 8 wt % to about 17 wt % nickel. The surface modified layer may include about 50 wt % to about 75 wt % copper. In some cases, the copper content of the surface modified layer may be high due to copper in the base copper alloy melt and / or copper particles in the slurry. The surface modified layer may include about 2 wt % to about 20 wt % zinc. The surface modified layer may include about 2 wt % to about 4 wt % Sn. The surface modified layer may include about 0 wt % to about 3 wt % bismuth. The surface modified layer may include about 0 wt % to about 9.0 wt % silicon, or about 3 wt % to about 9.0 wt % silicon.

[0104] As compared to the underlying copper-based alloy, the surface modified layer may be enriched in one or more components present in the slurry containing surface modifying materials used in manufacturing the articles. For example, the surface modified layer may be enriched in oxygen, aluminum, nickel, carbon, silicon, bismuth, or any combination thereof. In some cases, the ratio of the weight percent of an enriched element in the surface compared to the weight percent of the same element in the base copper-based alloy is above about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, or substantially infinite in the case where the surface-enriched element is not present in the base copper-based alloy.

[0105] In some cases, the surface modified layer may be depleted (i.e., have a reduced amount) in one or more components present in the copper-based alloy used to manufacture the articles. For example, the surface modified layer may be depleted in copper, zinc, tin, bismuth, or any combination thereof, as compared to the composition of the copper-based alloy used to manufacture the articles. In some cases, the ratio of the weight percent of a depleted element in the surface compared to the weight percent of the same element in the base copper-based alloy is below about 1, about 0.9, about 0.8, about 0.7, about 0.6, about 0.5, about 0.4, about 0.3, about 0.2, or about 0.1 or less.

[0106] In some cases, the corrosion rate of the corrosion resistant article is reduced by about 20% to about 95%, from about 45% to about 90%, as compared to the corrosion rate of the cast copper alloy component. In some cases, the corrosion-resistance article comprises a reduced leach rate of one or more elements into water, as compared to the leach rate of one or more elements into water of the cast copper alloy component.

[0107] The structure and composition of the surface modified layers on copper alloy articles disclosed herein are unique from the surface alloyed layers or surface composited layers formed by established methods of surface alloying and / or compositing, including laser surface alloying, electroplating, and gas-based surface alloying (e.g., carburizing or nitriding). This is because, for example, the conditions of formation of surface modified layers during the casting process of the disclosed technology are different than the conditions of formation of surface alloyed layers and surface composited layers formed by established processes. Additionally, established methods of surface alloying are significantly more expensive and, in some cases, can only produce a surface modified layer in regions of copper alloy articles which have a line of sight (e.g., an optically unobstructed path from a laser to a region of the copper alloy article). This is not a limitation of the methods and articles disclosed herein.

[0108] The methods and articles disclosed herein have several advantages over existing techniques. For example, surface alloying or surface compositing using the example processes described herein use less alloy material and result in lower costs compared to alloying the components throughout the cross section to improve their surface properties. Likewise, surface compositing using the example processes disclosed herein result in lower cost compared to adding particles or fibers throughout the cross section by utilizing less materials as compared to alloying or compositing the component throughout the entire cross section of the component.Example Embodiments

[0109] Embodiment 1: A low-cost method of producing a cast copper-based alloy component having an enriched, corrosion-resistant and wear-resistant surface, the method comprising:

[0110] (a) providing a copper-based alloy selected from the group consisting of yellow brass and red brass;

[0111] (b) preparing a slurry comprising:

[0112] at least one powder selected from the group consisting of Cu, Ni, Cu—Ni, Cu—Sn, Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and Ni-coated SiC; and

[0113] a binder medium selected from the group consisting of water-based or alcohol-based binders, or superplasticizer;

[0114] (c) coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold; optionally repeating coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold;

[0115] (d) heating the copper-based alloy to a temperature in the range of 1200° C. to 1300° C. or higher;

[0116] (e) pouring the molten copper-based alloy into the coated or mold optionally containing a slurry-coated core, whereby at least part of the powder interacts with the molten copper-based alloy at the surface; or the ceramic particle like graphite, alumina and silicon carbide in the slurry are incorporated in the surface of the casting forming a surface composited layer; and

[0117] (f) solidifying the copper-based alloy to produce a cast component having a surface alloyed layer that is chemically distinct from the bulk alloy and enriched in the elements provided by the powder and / or enriched in ceramic particles like graphite, silicon carbide, alumina or other ceramic or solid lubricating particles incorporated in the slurry and get transferred on the surface of the castings. The melt is poured in the mold in which the core is placed.

[0118] Embodiment 2: The method of embodiment 1, wherein the at least one powder comprises a mixture of copper and nickel powders in a ratio of about a 1:1 ratio to enrich the surface in nickel, thereby improving corrosion resistance in chlorine- or chloramine-rich environments.

[0119] Embodiment 3: The method of any one of embodiments 1 or 2, wherein the at least one powder further comprises bismuth (Bi) powder or a bismuth alloy to increase the bismuth content at the surface of the component, thereby enhancing surface-level machinability and chip formation, without the need of adding bismuth throughout the cross-section.

[0120] Embodiment 4: The method of any one of embodiments 1-3, wherein the at least one powder further comprises nickel-coated graphite powder, forming a surface composite with graphite inclusions that facilitate chip formation and improve machinability and reduce leaching of harmful elements into the water in contact with the castings during their use.

[0121] Embodiment 5: The method of any one of embodiments 1-4, wherein lead (Pb) is supplemented at the surface with or without a combination of bismuth (Bi) and uncoated or nickel-coated graphite, thereby eliminating or reducing the need for incorporating lead through the cross-section as in leaded brass alloys while improving machinability.

[0122] Embodiment 6: The method of any one of embodiments 1-5, wherein at least one powder comprises Cu—Sn powder to lower the zinc (Zn) concentration at the cast component surface, thereby enhancing corrosion resistance in aqueous environments.

[0123] Embodiment 7: The method of any one of embodiments 1-6, wherein the binder medium comprises polyvinyl alcohol (PVA) in about 4 wt % to about 8 wt %, diluted in water, to adhere the powder onto the core or mold surface.

[0124] Embodiment 8: The method of any one of embodiments 1-7, wherein the binder medium is selected from the group consisting of PVA, modified Refcobar 1010, modified Vibrantz, superplasticizer, or any combination thereof.

[0125] Embodiment 9: The method of any one of embodiments 1-8, wherein the slurry includes a plurality of powders selected from the group consisting of Cu, Ni, Cu—Sn (90Cu-10Sn), Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and uncoated or Ni-coated SiC or other powders, in order to form a composite or alloyed layer at the cast surface.

[0126] Embodiment 10: The method of any one of embodiments 1-9, wherein the slurry application is performed selectively on specific areas of the sand core or mold to produce localized regions of different surface chemistries on the cast component, tailored to the corrosive environment or application requirements or abrasive environment.

[0127] Embodiment 11: The method of any one of embodiments 1-10, wherein the thickness of the surface alloyed or composite layer is controlled by varying the amount of the powder or ceramic particles or the number of slurry coats applied to the core or mold.

[0128] Embodiment 12: The method of any one of embodiments 1-11, wherein the powders have particle sizes selected from the group consisting of about 149 μm for Ni, about 74 μm for Cu, about 74 μm for Cu—Sn, about 149 μm for Al, and about 36.5 μm for Ni-coated graphite.

[0129] Embodiment 13: The method of any one of embodiments 1-12, wherein the purity of the at least one powder is between about 95% and about 99.9%.

[0130] Embodiment 14: The method of any one of embodiments 1-13, further comprising pre-heating the coated core or mold at about 100° C. to about 400° C. for about 20 minutes to about 60 minutes or more to remove volatile components from the binder and reduce porosity in the surface alloyed layer.

[0131] Embodiment 15: The method of any one of embodiments 1-13, wherein the slurry-coated core or mold is dried at room temperature of about 20° C. to 25° C., or higher, overnight or longer, thus removing enough volatile content from the binder to mitigate porosity in the resulting surface alloyed layer.

[0132] Embodiment 16: An oxidation-resistant article comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0133] Embodiment 17: A wear-resistant article comprising a cast copper alloy component with a surface alloyed or a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0134] Embodiment 18: A lead leaching resistant article comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0135] Embodiment 19: An article with improved surface machinability comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0136] Embodiment 20: The method of Embodiment 1, wherein the particle size of Ni powder can be in the range of 50 μm to 175 μm, the particle size of Al powder can be in the range of 50 μm to 100 μm, the particle size of Cu powder can be in the range of 50 μm to 100 μm, the particle size of Bi powder can be in the range of 10 μm to 170 μm, the particle size of Cu—Sn powder can be in the range of 50 μm to 100 μm, the particle size of metal-coated Al2O3 powder can be in the range of 50 μm to 250 μm, the particle size of metal-coated graphite powder can be in the range of 16 μm to 200 μm and the particle size of metal-coated SiC powder can be in the range of 10 μm to 100 μm, and the powders are used to prepare the slurry applied on the mold and / or the core surface, as per Embodiment 1.

[0137] Embodiment 21: The copper alloy component can be cast to form a surface alloyed or surface alloyed composited layer with the addition of metal-coated graphite, metal-coated Al2O3 or metal-coated SiC or uncoated graphite, Al2O3 or uncoated SiC or other ceramic particles not mentioned in this literature or a combination thereof particles to the slurry.Miscellaneous

[0138] In the above detailed description, reference is made to the accompanying examples, appendices and drawings in which specific examples are shown by way of illustration. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the disclosure. It should be understood, however, that the detailed description and the specific examples, while indicating examples of embodiments of the disclosure, are given by way of illustration only and not by way of limitation. From this disclosure, various substitutions, modifications, additions rearrangements, or combinations thereof within the scope of the disclosure may be made and will become apparent to those of ordinary skill in the art.

[0139] Unless otherwise indicated, the various features illustrated in the drawings may not be drawn to scale. The illustrations presented herein are not necessarily intended to be actual views of any particular method, device, or system, but are merely idealized representations that are employed to describe various embodiments of the disclosure. Accordingly, the dimensions of the various features as illustrated may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., device) or method. In addition, like reference numerals may be used to denote like features throughout the specification and figures.

[0140] It should be understood that any reference to an element herein using a designation such as “first,”“second,” and so forth does not limit the quantity or order of those elements, unless such limitation is explicitly stated. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements.

[0141] Unless otherwise specified or indicated by context, the terms “a,”“an,” and “the” mean “one or more.” As used herein, unless otherwise limited or defined, “or” indicates a non-exclusive list of components or operations that can be present in any variety of combinations, rather than an exclusive list of components that can be present only as alternatives to each other. For example, a list of “A, B, or C” indicates options of: A; B; C; A and B; A and C; B and C; and A, B, and C. Correspondingly, the term “or” as used herein is intended to indicate exclusive alternatives only when preceded by terms of exclusivity, such as “only one of,” or “exactly one of.” For example, a list of “only one of A, B, or C” indicates options of: A, but not B and C; B, but not A and C; and C, but not A and B. In contrast, a list preceded by “one or more” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of any or all of the listed elements. For example, the phrases “one or more of A, B, or C” and “at least one of A, B, or C” indicate options of: one or more A; one or more B; one or more C; one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C. Similarly, a list preceded by “a plurality of” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of each of multiple of the listed elements. For example, the phrases “a plurality of A, B, or C” and “two or more of A, B, or C” indicate options of: one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C.

[0142] As used herein, “about,”“approximately,”“substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of these terms which are not clear to persons of ordinary skill in the art given the context in which they are used, “about” and “approximately” will mean plus or minus ≤10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.

[0143] As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising” in that these latter terms are “open” transitional terms that do not limit claims only to the recited elements succeeding these transitional terms. The term “consisting of,” while encompassed by the term “comprising,” should be interpreted as a “closed” transitional term that limits claims only to the recited elements succeeding this transitional term. The term “consisting essentially of,” while encompassed by the term “comprising,” should be interpreted as a “partially closed” transitional term which permits additional elements succeeding this transitional term, but only if those additional elements do not materially affect the basic and novel characteristics of the claim.

[0144] Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”

[0145] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0146] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0147] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0148] Other examples and uses of the disclosed technology will be apparent to those having ordinary skill in the art upon consideration of the specification and practice of the invention disclosed herein. The specification and examples given should be considered exemplary only, and it is contemplated that the appended claims will cover any other such embodiments or modifications as fall within the true scope of the invention.

[0149] The Abstract accompanying this specification is provided to enable the United States Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure and in no way intended for defining, determining, or limiting the present invention or any of its embodiments.EXAMPLESExample 1: Surface Alloying and Surface Compositing of a Brass Alloy Castings Using Mold and Core Coatings

[0150] This work presents a low-cost casting process for surface alloyed surface compositing (SASC) of C89836 brass castings. Surfaces of the sand cores were coated with slurries containing varying amounts of Cu, Ni, and reinforcement particles, including Ni-coated Al2O3 and Ni-coated SiC powders, before pouring brass melts into the molds. In SASC samples, Al2O3 and SiC particles were concurrently incorporated into the casting surface, forming a surface composited region. Microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed the formation of a Ni-enriched surface and the successful incorporation of SiC or Al2O3 particles on the casting surface. Electrochemical testing indicated that SASC castings containing Al2O3 and SiC particles exhibited reduced corrosion rates compared to the base alloy. The SA and SASC do not show any delamination when exposed to 250° C. In addition, the size of machining chips was much smaller in SASC, compared to the base alloy. These results demonstrate the potential of SASC as cost-effective routes for producing high-performance surface composited brass components with enhanced corrosion resistance using a single-step casting process.Introduction

[0151] Surface alloying can modify the surface of a base alloy by enriching the surface in Cu, Ni, or Cr to improve wear resistance, hardness, corrosion resistance and resistance to leaching of lead into water. It modifies surface composition and properties near the surface without altering the bulk casting, offering a cost-effective way to enhance performance by selectively alloying surface layers and reducing the need for expensive alloying elements throughout the cross-section of castings. Surface-alloyed components can be used in automotive, aerospace, tooling, and water industry applications. For brass components, surface alloying with Ni, Cr, and B using lasers has improved corrosion resistance; however, laser processing is costly and requires direct line of sight. Researchers have also explored diffusion coating, friction stir processing, and electron beam melting for surface alloying, but all the processes are expensive, require a line of sight, and / or require post-processing.

[0152] Surface alloying can be commercially valuable for brass components used in water systems because it prolongs component life, reduces maintenance costs, and ensures compliance with water safety regulations. Early studies linked chloramine in water to accelerated impingement attack and cavitation; others showed that brass faucets lasted three times longer without chloramine in water. Copper corrosion is strongly pH-dependent, with higher pH reducing chlorine-induced leaching. Later work suggested corrosion begins with oxidative attack by free chlorine, followed by dissolution of products, and is promoted by higher ionic strength, inorganic carbon, and temperature. Diffusion within oxide films slows overall corrosion. Alloying throughout the cross-section, as in Monel or Red Brass, shows superior water-corrosion resistance as compared to yellow brass.

[0153] A prominent corrosion mechanism in brass is dezincification, which involves the selective removal of Zn from the alloy surface exposed to the corrosive medium, resulting in a porous copper structure. This process occurs as Zn is more reactive than Cu and is more easily oxidized and dissolved in water, especially in the presence of slightly acidic or basic conditions. To prevent dezincification in brass alloys, inhibitors such as Arsenic (As) and Tin (Sn) have been added. Arsenic reduces Cu ions to form a protective cuprous oxide layer, while tin creates a film at grain boundaries to inhibit zinc diffusion. Using brass with lower Zn content or applying protective coatings can also help mitigate these corrosion processes. In chloride solutions at 68 F (20 C), α-brasses are prone to dezincification, particularly in stagnant areas and at elevated temperatures, even under flowing conditions. Dezincification is most severe in (α+β) and β-brasses. Brasses containing less than 30 wt % Zn predominantly form the α-phase and thus exhibit greater resistance to dezincification. Taps of red brass and Monel alloys have shown much longer life than yellow brasses, suggesting that higher Ni and Cu contents reduce corrosion. It is anticipated that surface alloying and surface compositing will also reduce dezincification since the surface will be enriched in copper, nickel and ceramic particles.

[0154] Leaching in brass alloys often results in the release of Pb and Cu ions into water, particularly under soft, corrosive conditions. Leaching is most pronounced during the first 24 hours of water stagnation, and regular flushing is an effective way to reduce metal concentrations. Adjusting the pH to around 7.5 or higher, maintaining sufficient alkalinity, and using orthophosphate as a corrosion inhibitor can further reduce lead and copper leaching by forming protective layers on the metal surfaces.

[0155] Lead has traditionally been added to brass to improve machinability by forming discrete particles that act as solid chipbreaks, resulting in smaller chips, smoother surface finish, and reduced tool wear. Even now when lead is not added as a deliberate alloy addition to improve machinability, there is residual lead in the plumbing fixtures due to the use of recycled material, and this can result in a leaching of undesirable amount of lead in water. It is anticipated that surface alloying and surface compositing will also reduce leching of lead in water. There has been considerable work on incorporating hard particles like Al2O3 and SiC through the bulk cross-section of copper alloys using powder metallurgy techniques. Prior research has shown that incorporating ceramic particles, such as Al2O3, into the matrix of copper alloys increases hardness and contributes to high-temperature stability and oxidation resistance. Al2O3 can lead to substantial increases in strength and hardness, for example, the addition of 4 wt % Al2O3 has been shown to cause a 63% increase in hardness and a 136% increase in yield strength, attributed primarily to Orowan strengthening and load transfer. Wear rates of copper alloys decrease by nearly 50% when Al2O3 is incorporated in the matrix of copper alloys. However, its abrasive nature can sometimes lead to higher coefficients of friction, and particle agglomeration can cause pull-out, accelerating wear through “three-body abrasion.” Al2O3 is the preferred reinforcement for increased corrosion resistance of brass alloys due to its dielectric nature and its compatibility with the formation of passive films, thereby enhancing the surface barrier properties. It acts as a physical obstacle, impeding the diffusion of zinc atoms and ingress of chloride ions, thereby mitigating dezincification and decreasing the corrosion rate in aggressive environments. Additionally, Al2O3 is useful for mitigating the release of heavy metals, such as lead (Pb), from brass into drinking water. Al2O3 works by physically covering exposed lead globules that effectively trap the lead. Anodic coatings using aluminum species have demonstrated nearly a 90% reduction in lead leaching.

[0156] Silicon Carbide (SiC) is known for its superior hardness and thermal conductivity compared to alumina. Incorporation of SiC particles in copper alloys leads to extreme abrasion resistance and high load-bearing capability in brass matrices. Incorporation of SiC in the matrix of copper alloys often leads to a low coefficient of friction (COF) in surface nanocomposites. SiC is considered to be a superior reinforcement in copper alloys for tribological applications, shifting the failure mode from severe adhesive wear to mild abrasive wear significantly extending component life. In terms of corrosion properties, SiC is a semiconductor, meaning it can theoretically form micro-galvanic couples with the conductive copper matrix, potentially accelerating the dissolution of the surrounding anodic brass. However, SiC-reinforced copper alloys have been shown to possess superior general corrosion resistance compared to unreinforced alloys.

[0157] Incorporation of SiC or Al2O3 particles throughout the cross sections of copper alloy components to get improved properties is expensive and presents additional challenges in processing of components reinforced throughout the cross section of the castings.

[0158] In this work, a technique for surface alloying and surface compositing of copper alloy sand castings is described, in which Al2O3 or SiC particles can be incorporated near the surface of the castings and alloyed to enrich Nickel and Copper. The technique involves coating molds or cores with slurry containing metal powders such as Ni and Cu (for surface alloying) and Ni-coated alumina and Ni-coated SiC particles (for surface compositing). When molten metal is poured into the mold containing slurry-coated cores on the surface enriched in Ni and Cu (Surface Alloying), Al2O3 or SiC particles are incorporated near the surface (surface compositing) when Ni-coated Al2O3 or Ni-coated SiC particles are present in the slurry. The microstructure, chemical composition, and phases present in the surface alloyed and surface composited layers have been characterized, and improvements in corrosion resistance have been demonstrated. In addition, increase in hardness, adequacy of adhesion between SA and SASC, layers and reduction in size of machining chips has been characterized. This technique represents an improvement over stir mixing and casting, since Al2O3 or SiC, Ni, and Cu are incorporated only near the surface, where they are needed for corrosion resistance, thereby reducing the amounts of Ni, Cu, and alumina or SiC required in through-alloyed and through-composited castings. The surface alloying and surface compositing technique can be readily adopted for sand-cast copper alloy components.Materials and Methods

[0159] Sand cores were coated with slurries containing metallic powders to form an in-situ coating layer on industrial cast components. Each core was coated with two layers of a graphite-based mold and core wash (Technikoat, HA International) to minimize reactions between the molten metal and the core sand, followed by drying under ambient conditions for 24 h. The cores were subsequently coated with a slurry consisting of Ni and Cu powders, Ni-coated Al2O3 or Ni-coated SiC particles, and a water-based binder system comprising either polyvinyl alcohol (PVA) or a combination of PVA and a superplasticizer (Table 1). Nickel was incorporated to enhance corrosion resistance and to reduce potential leaching in Bi-containing brass. The binder was prepared by dissolving PVA powder in water at 80° C. to obtain a 10 wt % solution, after which the metallic powders were incorporated under constant manual stirring to ensure a homogeneous mixture. The metal powders (Ni and Cu) and Ni-coated alumina and SiC particles were measured in quantities shown in Table 1, and the binder was added while maintaining a constant stirring rate. The viscosity of the slurry binder was important, as low viscosity would lead to powder separation. The slurry containing metal powders and Ni-coated alumina and SiC powders was applied on the surface of the cores to form a coating. The coated cores were dried at room temperature for 48 h and then placed into the sand mold. The C89836 alloy melt (at 1200° C.) with the composition listed in Table 2 was subsequently poured into the mold. A schematic illustration of the manufacturing process is presented in FIG. 2.TABLE 1Samples made and the quantities of Ni and Cu powders and Ni-coatedreinforcements used for slurry preparation for coating on cores.Slurry Composition of Core CoatingSampleReinforcementNiCucodeBase alloyBinderReinforcementPowder (g)Powder (g)Powder (g)YBYellow Brass—————S0C89836—————S1C89836PVANi-coatedS2C89836PVA + alumina3.16855SuperplasticizerparticlesS3C89836PVANi-coated SiCS4C89836PVA + particlesSuperplasticizerTABLE 2Elemental composition of base UNS C89836 alloy.ElementCuPbSnZnFePNiAlBiSSbSiMin (%)87.0—4.02.0————1.5———Max (%)91.00.257.04.00.350.060.90.0053.50.080.250.005FIG. 3 shows SEM images of the powders used to make the slurry. FIG. 3 (a)-(d) shows the morphology of the particles, including pure Cu, pure Ni, Ni-coated SiC, and Ni-coated Al2O3, respectively. To show the coating of nickel on Ni-coated powders, they were mounted in epoxy resin using a hot-mounting machine, then ground to a flat surface, and their cross-sections were observed. FIG. 3 (e)-(e3) shows SEM images and elemental mapping of Ni-coated SiC particles, revealing a Ni coating layer with varying thickness. FIG. 3 (f)-(f3) shows the cross-sectional SEM images and elemental mapping of Ni-coated Al2O3 particles, demonstrating a continuous Ni coating on the particle surfaces.

[0161] The castings were sectioned from the SASC regions for metallographic characterization. Samples were cut and mounted in conductive phenolic resin and ground sequentially with SiC abrasive papers of 180-1200 grit. Final polishing was performed using a 1 μm alumina suspension followed by 0.05 μm colloidal silica to obtain a mirror finish. The polished samples were etched with Copper No. 2 (15 mL FeCl3, 15 mL HCl, 100 mL H2O) to reveal the microstructure. Optical microscopy was conducted using a Nikon EPIPHOT 300 microscope under polarized light, while microstructural features were further examined with a JEOL 6460LV scanning electron microscope (SEM) using backscattered (BSE) and secondary electron (SE) imaging. Phase identification was conducted via XRD using a Bruker D8 Discover system, which was equipped with a Ni filter and Cu target and operated at 40 kV and 40 mA. The machinability test was performed using a sweeping tool with a depth profile of 0.254 mm on the samples to evaluate the chip formation behavior.

[0162] Image analysis was performed in ImageJ using a combination of automatic thresholding and manual selection to calculate the area percentages of phases, the size of reinforcement particles, and the size of select phases. Potentiodynamic polarization testing was performed to characterize the corrosion resistance of the samples. Corrosion tests were performed using a potentiostat (SP-200, BioLogic) with tap water at room temperature, containing an estimated chloramine concentration of approximately 2 ppm, as the electrolyte and an exposed surface area of 0.980 cm2 as the working electrode. The SASC samples and platinum wire mesh were used as the working electrodes and counter electrode, respectively, while Ag / AgCl was used as the reference electrode.Results and Discussion

[0163] The presence of a Ni coating on both SiC and Al2O3 particles promoted the formation of a Ni-enriched surface layer on the cast brass components. This SASC layer improved the corrosion resistance of the castings while reducing overall production costs by forming a thin, in-situ-formed surface layer, instead of adding nickel throughout the cross-section. In addition, incorporating ceramic reinforcements, such as SiC and Al2O3, was expected to further reduce corrosion rates and enhance wear resistance by reducing abrasion. SiC has a density of 3.15 g / cm3 and a hardness between 9-10 on the Mohs scale, while Al2O3 has a density of 3.21 g / cm3 and a hardness of 9 on the Mohs scale. Both reinforcement particles had lower densities and higher hardness than brass alloys. Prior work on copper-ceramic composites has shown that lower-density reinforcement particles, such as graphite, Al2O3, or SiC, tend to agglomerate and float to the top of the melt during stir-casting and solidification. The problem of the flotation of reinforcement particles during stir casting is eliminated using the surface composting process described in this work.

[0164] FIGS. 4 (a) and 4(b) show the optical microstructure of the SiC SASC layer formed in situ as a result of the interaction between the molten brass and the slurry-coated core containing SiC reinforcement in the form of Nickel-coated SiC powder and Nickel and Copper powders. The SiC particles were distributed throughout the SASC layer, forming a localized surface-composite layer rich in nickel and SiC particles. The SiC particles were coated with a Ni layer to improve wetting between the melt and the SiC particles and to help improve the bonding. The Ni powder and the Ni coating on the SiC particles dissolved in the brass melt, thereby enriching the surface composited layer with up to 10.69 wt % Ni, which was significantly higher than the 0.9 wt % Ni originally present in the base alloy. FIG. 4(c) shows the area elemental analysis of the SiC-reinforced SASC layer compared with the base alloy. The Ni content in the SASC layer reaches 10.69 wt %, whereas no measurable Ni is detected in the base alloy. Importantly, the SASC process does not significantly alter the concentrations of other alloying elements, such as Bi and Sn, which remain within approximately the same compositional range in the surface alloyed and surface composited layer as they were in the base alloy. FIG. 4(d) also shows the elemental analysis of the phases present in the SASC layer; the lighter phases are uniformly dispersed Bi-enriched precipitates throughout the SASC layer. The Bi-rich precipitates were also located within the Ni-rich islands and in the matrix. The Bi originally present in the base alloy is also incorporated in the SASC layer.

[0165] Elemental mapping of the SASC layer revealed a high concentration of Ni-rich islands in the region between the SiC and Al2O3 particles (FIG. 4 (e)-(e4) and FIG. 4 (e)-(e4)) apparently, as the base alloy melt comes into contact with the metal-coated ceramic powder slurry, the heat from the molten metal melts the Cu powder in the slurry. Simultaneously, the Ni powder and the Ni-coating on the SiC or Al2O3 particles dissolve in the Cu-rich molten metal solution. The melt at the mold-metal interface becomes enriched in Ni, thereby altering the local composition to a Cu—Ni—Zn alloy. The present solidification hypothesis suggests that the Ni-rich islands are the primary phase to form during solidification in the SASC region of the melt. As the phase grows, the reinforcement particles, SiC or Al2O3, are pushed by the growing phase, leading to the observed concentrations of these particles between Ni-rich islands. The pushing of reinforcement particles between Ni-rich islands was more prominent in samples with SiC, as the particle size was smaller than the Al2O3 particles, and SiC has a lower density than Al2O3. The Ni coating on SiC particles was 60% and 25.7% on Al2O3 particles by weight. Thus, the overall Ni concentration in the SASC layer differed between the samples containing SiC and Al2O3 particles. The ternary phase diagram of the Cu—Ni—Zn system suggests that a phase is formed at the start of solidification, which is a solid solution of Cu—Ni—Zn. As the Ni in the SASC zone is trapped in this solid solution, the remaining melt, now depleted in Ni, solidifies to form a Cu—Zn solution.

[0166] The microstructures of the SASC layer incorporating Al2O3 particles are shown in FIG. 5. FIGS. 5(a) and 5(b) show OM images of the Al2O3 SASC in low and high magnifications, respectively. The bright areas represent the Ni-rich island formed due to the Nickel coating on the Al2O3 particles, as the nickel powder in the slurry. FIG. 5(c) shows the EDS analysis of the SASC layer and the distribution of alloying elements, including Ni added as a powder and due to the use of Ni-coated Al2O3 particles. The concentration of Ni ranges from 9.57 wt % to 14.74 wt % in the SASC layer, compared to 0.66 wt % to 1.96 wt % in the base alloy. A higher Ni wt % in the SASC layer indicated the dissolution and subsequent alloying of Ni from the reinforcement particles with the S0 melt. Although the Ni concentration in the SASC layer was lower than that of Monel alloys, a higher wt % of Ni in the SASC layer (than that of the base alloy) is expected to improve corrosion resistance, including chlorine or chloramine-rich environments. The microstructures showed a Ni-rich layer at the particle periphery. In the Al2O3-incorporated samples, when Ni-coated Al2O3 was incorporated into the SASC layer, a nickel-enriched zone remained around the alumina particles, measuring around 13 μm in thickness. Elemental mapping of the microstructure near the particles revealed a Ni rich layer along the perimeters of the Al2O3 in the SASC layer.

[0167] Microstructural studies revealed that a Ni-depleted zone formed around the Ni-rich islands, observed in both SiC- and Al2O3-reinforced samples. The Ni-depleted zone is the area surrounding the SiC or Al2O3 particles, low in Ni content due to the formation of Ni-rich islands. Reinforcement particles were present only in the SASC layer of both samples, (with no reinforcement particles or Ni enrichment observed in the base alloy below the SASC layer). This suggested that the cooling rate of the melt did not lead to significant flotation of the particles, as the density of the reinforcement particles was lower than that of the melt. The average distance between the SiC particles and the periphery of the Ni-rich islands was approximately in the range of 20-25 μm. This distance also corresponded to the thickness of the Ni-depleted zones surrounding such Ni-rich phases. The size of the SiC particles was approximately 25 μm while that of the Al2O3 particles was approximately 200 μm. Prior work on the solidification of composite materials has shown that the presence of reinforcement particles can restrict the growth of the matrix microstructure, including dendrites. The growth restriction is based on the alloy's cooling rate, as the dendrite size correlates with it.

[0168] FIG. 6(a)-6(b) shows the area fraction composition for Ni-rich islands, reinforcement (Al2O3 or SiC) and Bi precipitates on the SASC layer. The S2 sample showed the highest ceramic particle reinforcement area percentage, around 19%. All samples had Ni-rich islands with an area percentage of around 10-13%. FIG. 6(c)-6(d) shows the average sizes of the Ni-rich islands, reinforcement particles, and Bi precipitates in the SASC layer. The average size of the Ni-rich islands was consistent through the SASC layers of all samples, irrespective of the chemistry of the reinforcement particles. These Ni-rich islands did not contain any reinforcement particles, suggesting that the formation of the phase and its subsequent growth pushed the SiC or Al2O3 particles to regions between Ni-rich islands.

[0169] FIG. 6(b) shows the area percentage of bismuth (Bi) precipitates across the different composite samples. The Ni—Cu+Ni—SiC (PVA) sample has the highest concentration of these Bi precipitates. When the superplasticizer is added to this SiC system, the area fraction of Bi precipitates drops by about half to 0.50%. For the Al2O3 composites, the trend is reversed. The PVA-only sample has 0.48% area containing Bi, which increases to 0.70% when the superplasticizer was used. The precipitation of Bi is favored at the grain boundaries in brass alloys with low wt % of Ni. In the presence of Sn, the precipitation of Sn at the grain boundaries is favored over Bi, which can restrict the sites available for the precipitation of Bi. Prior work suggests that the presence of Sn in the alloy affects the precipitation of Bi at grain boundaries, as Sn preferentially precipitates there, preventing Bi segregation. The samples studied showed nucleation of Bi precipitates within the Ni-rich islands in select instances. As the size of the SiC particles and the wt % of Ni in the alloy increase, the formation of Bi bilayers is favored, as they are the thermodynamically stable and dominant interfacial phase at Ni and Cu grain boundaries.

[0170] The effect of Ni wt % in the SASC layer on the average size of Bi precipitates was observed in FIG. 6(d), where samples with Al2O3 as reinforcement had smaller precipitates than samples with SiC as the reinforcement. The SiC samples had a lower wt % of Ni in the SASC layer than the Al2O3 samples, and the Bi precipitates were observed to preferentially nucleate along the SiC particles. Specifically, the S3 sample has the largest average precipitate size at 5.32 μm2. This size decreases slightly to 4.22 μm2 when the superplasticizer is added to the SiC system. In the S1 and S2 samples, the precipitates remain quite small, measuring 1.13 μm2 for the PVA sample and 1.42 μm2 for the superplasticizer sample.

[0171] In FIG. 7(a), most samples showed a thickness of SASC layers of around 1000 μm, with S4 reaching a maximum thickness of 1284 μm. Prior studies have shown that the thickness of the SASC layer can be a function of the quantity of slurry material applied to the mold or core surface. FIG. 7(b) shows the coverage of the SASC layer, defined as the fraction of the sample length covered by the SASC layer. The S1 sample exhibited nearly complete surface coverage (99.81%). In contrast, the lowest coverage was observed for the S2 sample (68.71%). This trend is consistent with the reduced thickness shown in FIG. 7(a) indicates the formation of a more fragmented composite layer. The periphery of the Al2O3 particles within the SASC layer exhibited a Ni-rich coating, indicating incomplete dissolution of the Ni layer in the melt. In contrast, such features were not observed for the SiC particles. FIG. 7(c) shows the Ni shell thickness, a measurement observed in the S1 and S2 samples containing the Ni-coated Al2O3 particle reinforcement, alongside the Ni-depleted length, a measurement observed in the S3 and S4 samples containing the Ni-coated SiC particle reinforcement. For S1 and S2, a Ni rich layer of approximately 13 μm was observed around the Al2O3 particles. In contrast, the Ni-depleted length, representing the average distance between Ni islands and SiC particles, varied between the SiC-reinforced samples. S3 exhibited a higher depletion length of ~25 μm, while S4 showed a reduction to ~20 μm, indicating a more densely packed distribution of SiC particles around Ni islands. The superplasticizer used in this study, MEGAPOL GUSR-AC, assists the dispersion of particles, in this case Al2O3 and SiC, reducing particle agglomeration and improving the fluidity of the slurry. An increase in particle dispersion had different effects on the Al2O3 and SiC slurries due to differences in their particle size. The large-sized Al2O3 particles, present in a highly fluid medium, were assumed to be highly dispersed over the applied core surface, leading to a thinner SASC layer and a lower coverage % of the formed SASC layer. The smaller SiC particles exhibited the opposite trend, forming a thick SASC layer with higher coverage.

[0172] FIG. 8 shows the average corrosion current density (Icorr) for the cast samples. A higher Icorr corresponds to a higher corrosion rate (i.e., lower corrosion resistance); the comparison directly reflects material performance. The YB (yellow brass) sample exhibits the highest corrosion rate, with an Icorr of approximately 1.33 μA / cm2. In contrast, the S0 sample (red brass) shows a 46% reduction in Icorr, reaching 0.73 μA / cm2. This reduction is associated with a lower dezincification rate in the corrosive environment, resulting in a shallower dezincified layer and, consequently, higher corrosion resistance. This behavior can be attributed to the more negative standard electrode potential of Zn (E=−0.763 V) compared with Cu (E=+0.337 V). The large potential difference promotes the preferential dissolution of Zn in corrosive environments, leading to severe dezincification in Zn-rich alloys such as yellow brass. This finding is also consistent with prior literature showing that red brass has considerably higher corrosion resistance than yellow brass. The coated samples exhibited higher corrosion resistance and lower Icorr, with reductions for S1, S2, S3, and S4 compared to S0, respectively. This can be attributed to the formation of Ni-enriched, approximately 10-13 wt %, for continuous and thick SASC layers on the cast components.

[0173] Comparing the electrochemical potentials of Ni and Cu, Ni exhibits a more negative potential than Cu; therefore, Ni is preferentially oxidized in a corrosive environment. The interaction between Cu and chloride ions can be described by the following reaction:

[0174] The solubility of this product is negligible; therefore, it deposits on the sample surface, forming a porous CuCl film.

[0175] Subsequently, hydrolysis reactions may occur, leading to the formation of an oxide passive Cu2O layer on the Cu surface:

[0176] In the absence of Ni, the adsorption of Cl− accelerates the diffusion of metal ions from the metal / passive film interface toward the film / solution interface. This enhanced diffusion leads to the formation of cation vacancies, which promotes pitting initiation and ultimately results in the breakdown of the oxide passive film. However, in the presence of Ni, Ni atoms dissolved into the SASC layer or Ni-rich islands provide a sufficient supply of Ni that can segregate into the oxide passive film through a solid-state reaction and incorporate into the cation vacancies. This incorporation competes with the injection of Cu cations into the oxide passive layer, thereby diminishing pitting and reducing the corrosion rate of SASC cast components.

[0177] FIG. 9 shows the difference in hardness between the various SASC layer types (S1-S4) and the S0 base alloy (S0). All the SASC layer samples showed an increase in hardness compared to the S0 base alloy, which has a hardness value of 81 HV. The highest Vickers hardness value was for sample S4, at 138 HV. As discussed in prior sections, SiC and Al2O3 have higher hardnesses than the C89836 base alloy and an increase in the hardness of the SASC layer is expected. The incorporation of the particles hinders the deformation of the matrix under loading, transferring the load from the matrix to the reinforcement and thus increasing hardness. This was shown in prior work where incorporation of Aluminum Nitride (AlN) up to 12 wt % in brass alloys led to a 38.57% increase in hardness. Brass composites reinforced with SiC whiskers exhibited a 160% increase in the hardness at 40 vol % reinforcement, but experienced a decrease in hardness following 42 vol % reinforcement. These results show that the presence of reinforcement particles in the SASC layer improved the surface hardness of the castings. The hardness of the Al2O3-containing samples was within a 5% range of the samples with and without superplasticizer. In the samples incorporating SiC, the difference in hardness values was approximately 30% between the sample without superplasticizer (S3) and the sample with superplasticizer (S4). This may be due to the differences in the microstructures of samples S3 and S4. The average size of Ni-rich islands was higher in sample S4, the average size of Bi precipitates was lower for sample S4, and the area % of Bi precipitates was also lower for sample S4.

[0178] FIG. 10 shows the X-ray diffraction used to identify the phases formed in the surface-alloyed / surface-composited layer. SiC peaks and Al2O3 peaks were observed, confirming the incorporation of SiC and Al2O3 particles in the SASC layers. The Ni-rich islands, containing Ni, Cu, and Zn with different stoichiometric compositions including Cu0.95Ni0.05 and Cu2NiZn are identified. Other peaks corresponding to Sn and Bi in the S0 bulk alloy were also present in the XRD pattern as the Bi and Sn0.05Ni0.95 phases. These results confirm the transfer of Al2O3 or SiC particles from the slurry-coated cores to the surfaces of the castings, as well as the enrichment of the casting surfaces with Nickel and other metallic powders present in the slurry.

[0179] FIG. 11 shows optical microscopy images of samples S1 and S3 after performing the qualitative adhesion test of metallic coatings as per ASTM B571. The testing cycle consisted of heating the samples to a set temperature (a) 250° C. and (b) 400° C. and rapidly cooling them via a water quench. Because the composition of the SASC layer differs from that of the base alloy, the coefficient of thermal expansion (CTE) differs. Thus, as the sample was heated and rapidly cooled, the delamination of the SASC layer from the base alloy could occur. Additionally, the heating may affect the interface between the SASC layer and the base alloy. Results of sample S1 show the (FIG. 11, panel a1) as cast condition, (FIG. 11, panel a2) after heating treatment after* 250° C., and (FIG. 11, panel a3) after heating to 400° C. and instantly cooling to room temperature by water quenching. There does not appear to be any visible change in adhesion between the interface of the SASC layer and base alloy layer compared to the as-cast specimen. Results of sample S3 show the (FIG. 11, panel b1) as cast condition, (FIG. 11, panel b2) heating to 250° C. followed by quenching, and (FIG. 11, panel b3) heating to 400° C. followed by quenching. Between the 250° C. and 400° C. heat treatment images, there are no visible alterations between the interface of the SASC layer and base alloy layer compared to the as-cast specimen. Porosity present in FIGS. 11(b1) and 11(b3) is present at alternating times between polishing processes of the samples.

[0180] FIG. 12 compares chips collected during machining of four copper-based samples including 12(a) yellow brass, 12(b) base alloy C89836, 12(c) C89836+SA Layer, and 12(d) C89836+SASC layer (Ni—Al2O3). A drill bit was swept across each surface at a cutting depth of 0.010 in so that only the SA or SASC layer was machined. Optical images are shown for Yellow Brass 12(a), C89836 alloy 12(b), Ni—Cu SA layer 12(c), and sample S1 SASC layer with Al2O3 particles 12(d). Machining of Yellow Brass 12(a) produced long, continuous ribbons, reflecting high ductility and poor chip breakage, making it difficult to machine. C89836 alloy 12(b) formed shorter, more fragmented chips, an effect attributed to bismuth additions that aid chip breakage. In contrast, the chips in SA layer were smaller than C89836 alloy and the S1 SASC layer with Al2O3 particles 12(d) lead to the formation of the smallest and most granular chips, consisting of short segments and fine particles. This suggests that Al2O3 particles act as chip breakers, resulting in smaller chips. Overall, chip size decreased progressively from Yellow Brass to C89836, to Ni—Cu SA, and finally to S1 SASC, demonstrating a clear trend toward smaller and more granular chips.

[0181] The results show that smaller machining chips generally achieved by adding Pb or Bi to copper alloys may be achieved by incorporating Ni and Al2O3 into a SASC layer. This may provide a path to replace toxic and expensive alloying elements like Pb and Bi with a low-cost and safer alternative.CONCLUSIONS

[0182] A one-step casting process was developed to synthesize functionally graded surface alloyed (SA) and surface alloyed and surface composited (SASC) C89836 brass castings. This was achieved by coating sand cores with slurries of Ni and Cu powders combined with Ni-coated Al2O3 or Ni-coated SiC powders and then placing them in the mold prior to pouring molten copper alloy.

[0183] The SASC layers successfully formed on the surface of the cast brass components using this process.

[0184] When slurry-coated cores were incorporated in the mold prior to pouring the molten alloy, the interior surface of the castings was successfully surface alloyed and surface composited.

[0185] Optical and electron microscopy studies showed that the surface alloyed and surface composited layers in the surface of the castings were enriched with nickel and copper, and they had significant volume percentages of Al2O3 or SiC particles incorporated in the SASC layers.

[0186] The SASC layers containing Ni, Al2O3 or SiC particles exhibited higher hardness due to the successful incorporation of the SiC and Al2O3 ceramic particles into the matrix.

[0187] The copper alloy castings with SASC surface layer showed reduced corrosion rates compared to the base copper alloy. These castings are also likely to exhibit reduced leaching rates of harmful elements in water.Supporting InformationTABLE 4Bulk Composition of Ni-Al2O3 SASC with PVA from EDS AnalysisComposition(wt %)OAlNiCuZnSnBiSurface8.85 ± 2.6716.06 ± 3.7614.74 ± 1.78 55.03 ± 4.18 3.04 ± 0.592.29 ± 0.120.00 ± 0.00 Base0.33 ± 0.33 0.00 ± 0.00 0.66 ± 0.6686.23 ± 0.57 4.98 ± 0.394.84 ± 0.112.98 ± 0.14TABLE 5Bulk Composition of Ni-Al2O3 SASC with PVA + Superplasticizer from EDS AnalysisComposition(wt %)OAlNiCuZnSnBiSurface9.06 ± 0.0318.82 ± 0.0112.56 ± 0.94 51.60 ± 0.29 3.18 ± 0.95 3.16 ± 0.14 1.63 ± 0.16 Base0.00 ± 0.00 0.00 ± 0.00 1.09 ± 0.0986.45 ± 0.125.19 ± 0.685.26 ± 0.232.03 ± 0.71TABLE 6Bulk Composition of Ni-SiC SASC with PVA from EDS AnalysisComposition(wt %)CSiNiCuZnSnBiSurface5.54 ± 0.38 4.82 ± 1.77 9.57 ± 1.6272.57 ± 2.16 4.60 ± 0.82 3.73 ± 0.19 1.23 ± 0.47 Base3.86 ± 0.661.54 ± 1.541.96 ± 1.7082.30 ± 1.744.43 ± 0.804.51 ± 0.162.05 ± 0.56TABLE 7Bulk Composition of Ni-SiC SASC with PVA + Superplasticizer from EDS AnalysisComposition(wt %)CSiNiCuZnSnBiSurface6.76 ± 0.298.15 ± 0.2112.91 ± 0.66 63.39 ± 0.64 3.15 ± 0.043.44 ± 0.15 2.19 ± 0.19Base4.80 ± 0.100.00 ± 0.00 1.06 ± 0.5383.48 ± 0.425.36 ± 0.374.34 ± 0.230.96 ± 0.50Example 2: Factors Considered for Creating Alloyed and Composited Surface Layers on BrassIntroductionBrass components in water distribution systems are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from metal leaching.The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure. The proposed surface alloying process significantly enhances the durability of brass components by targeting corrosion reduction at its surface. This process is practical and cost-effective, easily integrated into existing foundries without additional equipment. This process involves casting components in molds and cores coated with a slurry containing alloying element powders, enriching the surfaces with elements such as Nickel, Copper, and Bismuth. This method is capable of surface alloying selected surfaces, including internal surfaces in contact with water, and enhancing corrosion resistance to levels comparable to more expensive materials like red brasses and Monel. The process does not require a line-of-sight of the target surface, allowing for the alloying of interior surfaces of complex castings.This approach offers several example benefits:1. Cost Reduction: By alloying only the surface of brass components, the process reduces the need for expensive alloying elements like nickel and copper, lowering production costs.

[0192] 2. Extended Component Lifespan: Improved corrosion resistance through surface leaching alloying significantly extends the lifespan of brass components, resulting in fewer maintenance disruptions and enhancing water distribution system stability.Feasibility Demonstration

[0193] Both yellow brass and bi-alloy red brass were used as base alloys, which were sand cast and alloying elements such as Cu, Ni, Al, and Cu—Sn were used for enriching selected cast surfaces. It was demonstrated that the incorporation of Ni and Cu—Ni powders in the surface alloyed layers lead to improved corrosion resistance of brass components-85% reduction in the corrosion rate of yellow brass and 70% reduction in the corrosion rate of red brass has been observed. The highest thickness of surface alloyed layers achieved was 2 mm in lab scale experiments, and the average thickness was 400 μm.

[0194] Following the demonstration of the feasibility of the surface alloying process both in the laboratory as well as in castings made on the industry floor, a design of experiments was formulated to identify the optimum process parameters for forming continuous surface alloyed layers. The parameters that were tested included melt temperature in the range of 1100-1200° C., mold temperature in the range of 25-125° C., and the ratio of weight percentages of Nickel and Copper proportional to the binder added to the slurry. It was observed that higher melt and mold temperatures and a ratio of 1:1 for Nickel and Copper powders were suitable for forming continuous surface alloyed layers. The elemental composition of the surface alloyed layer showed enrichment in nickel and copper, and the phases formed in the surface alloyed layer were identified. The improved corrosion resistance of the surface alloyed samples in a chloramine-rich aqueous environment was demonstrated compared to control samples of base alloys. The most suitable compositions for surface alloying were selected for an industrial pour at the Fall River Foundry, where the cores were coated with a slurry-containing metallic powders to form surface alloyed layers in the internal surface of the casting. Polyvinyl alcohol (PVA) was explored as the binder for the slurry instead of sodium polyacrylate and Refcohol to compare its effects on residual porosities. Preliminary results are shown in FIG. 13A-13C.

[0195] Investigations into corrosion on brass faucets showed that they were more durable in the absence of chloramine and that corrosion induced by chlorine was influenced by water pH. Further research showed that corrosion is initiated by the oxidative attack on the brass component's surface, followed by the dissolution of the oxidative products. Factors like ionic concentration and temperature were also found to promote corrosion, and the need for diffusion within the oxide layer acted as a retardant.

[0196] The approach used herein integrates surface alloying directly into the conventional casting process, increasing the weight percentage of Cu, Ni, and other selected elements on selected surfaces of cast water industry components and improving the corrosion resistance of yellow brass components. The higher zinc content in yellow brass makes it more susceptible to dezincification and corrosion, especially in chloride-rich, acidic, or high-temperature environments. By enriching the surface of yellow brass with copper through surface alloying, this work aims to create a red brass-like surface on yellow brass components and increase the corrosion resistance of yellow brass components. This process enhances the overall corrosion resistance of the components, leading to longer lifespans, reduced maintenance, and improved system reliability in the water industry.

[0197] Experiments will be aimed at understanding how varying parameters such as melt temperature, mold temperature, and alloying elements effect the corrosion resistance, hardness, adhesion, continuity, thickness, and as-cast finish of the surface alloyed layer. The slurry containing metal powder / s will be applied to selected surfaces of the molds and cores, and the molten metal will be poured. The variables to be controlled for in the experiments will be melt temperature, mold temperature, and slurry composition. After pouring, samples will be taken by bisecting the cast components through the surface alloyed layer. Samples will then be mounted and polished for surface analysis. The hardness test will be conducted on the surface alloyed layer to estimate the mechanical properties of the coated layer. Image analysis will be used to measure the porosity, the thickness of and the volume percentages of phases in the surface alloyed layer. Corrosion testing will be performed using the potentiodynamic test. The as-cast samples will be conditioned in tap water, as it contains the city-approved limits of chlorine and chloramine, for a period of 24-48 hours. Following this conditioning, the Icorr value of the surface alloyed layer and the base metal (yellow and red brass) will be measured.

[0198] The experiments will have a 4 lbs. melt size, with the melt heated to a maximum temperature of 1200 C. The molds, made using chemically bonded sand, will be coated with the metal powder-binder slurry and dried at room temperature. Further heating in a low-temperature furnace at a maximum temperature of 200 C will be performed under a fume hood in order to eliminate some of the gaseous products formed during the heating of the binder. The metallographic preparation will be done using industry-standard methods, and Cooper No. 2 etchant will be used to etch the base metal while leaving the nickel-enriched surface alloyed layer intact. Clemex Vision and ImageJ will be used for image analysis of the microstructure.

[0199] Advanced characterization methods such as Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM-EDS), and X-ray diffraction (XRD) will be used to quantify the chemical composition and identify the phases formed in the surface alloyed layer, respectively. The adhesion of the surface alloyed layer with the base metal will be estimated using temperature cycling. The as-cast sample will be heated, followed by rapid cooling in water. The effect of this sudden heating and cooling on the interface of the surface alloyed layer and base metal will be observed using microscopy.Contemplated Factors:1. Process optimization: The size and composition of the metal powders, melt temperature, the composition of the binder and ratios of said components will be optimized for the application of the metal-binder slurry on mold and core surfaces to get targeted thickness, continuity of surface alloyed layers with controlled microstructure, composition, and surface roughness to achieve targeted corrosion resistance. Statistical analysis will be done to quantify the increase in corrosion resistance.

[0201] 2. Defects: In order to improve the properties of the surface alloyed layer, the formation of defects will be minimized by optimizing the permeability of the mold, reducing the formation of volatile compounds from the slurry, and introducing venting in the molds or cores. The reduction in defects will be quantified.

[0202] 3. Targeted incorporation of bismuth into the surface alloyed layer by incorporating Bismuth powder with copper and / or nickel powder in the slurry coated on the molds and cores was done. As machining is often done only on the surface, incorporating Bismuth on selected surfaces using surface alloying will improve machinability, lowering the cost by eliminating the need to add Bismuth throughout the cross-section

[0203] 4. Testing the adhesion of the surface alloyed layer with the base metal casting: The surface alloyed casting will be cycled between high and low temperatures in accordance with ASTM standards. The components will undergo selected thermal cycling to confirm that separation does not occur between the surface alloyed layer and the base metal.

[0204] 5. Long-term and accelerated corrosion testing: The corrosion resistance will be tested over longer periods of time using accelerated tests or actual field applications in collaboration with industry partners. The objective will be to ensure the prototypes do not fail while operating in a flowing water environment for long periods, as opposed to static testing.

[0205] 6. Testing of surface alloyed prototypes cast for composition, phase analysis, surface hardness, and corrosion resistance.

[0206] 7. Exploring if as-cast surface alloyed layers can be retained after limited deformation processing in simple shapes to explore the applicability of surface alloying to selected wrought components used in the water industry.

[0207] 8. Optimize the size of metal powders and the composition of the slurry used to achieve surface alloyed layers with targeted thickness, continuity, surface roughness, and corrosion resistance.

[0208] 9. Optimize the microstructure of surface alloyed layers to maximize the corrosion resistance in chlorine and chloramine-rich aqueous environments.

[0209] 10. Optimize the binder medium used in the slurry for suspension of metal powders to reduce the formation of porosity in the surface alloyed layer.

[0210] 11. Incorporate Bismuth as an alloying element to improve the machinability of the surface alloyed layer and to reduce unit cost compared to products with Bismuth alloyed through the cross section.

[0211] 12. Demonstrate the adhesion of the surface alloyed layer to the base metal by subjecting surface alloyed castings to selected temperature cycles.

[0212] 13. Explore reducing wetting and imparting hydrophobicity to surface alloyed layers, especially in the interior of castings by controlling microstructure and roughness, and by incorporating hydrophobic reinforcements into surface alloyed layers.

[0213] 15. Demonstrate the improved corrosion resistance of surface alloyed samples and prototypes in laboratory and industrial environments using simulated tests.Example 3: Development of a Surface Alloying Technique to Enhance Corrosion Resistance in Brass Castings

[0214] This work explores a novel surface alloying technique aimed at improving the corrosion resistance of brass castings, particularly in chlorine-rich or chloramine environments. The proposed method offers a cost-effective approach to selectively alloy vulnerable regions during the casting process, even in areas without direct line of sight. By applying slurry coatings containing binders (modified Refcobar 1010 gel, Sodium Polyacrylate, Polyvinyl Alcohol, or modified Vibrantz binder) mixed with alloying powders (Cu, Ni, Sn, Al) onto cores, in-situ surface alloying was achieved.

[0215] Material Characterization through Optical Microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), hardness measurements, and corrosion analysis. Industrial-scale trials conducted at Fall River Foundry validated the feasibility of this technique. Results demonstrated minimal porosity and distinct alloyed layers, with XRD analysis identifying favorable compositions, including Copper-Nickel-Tin, Copper-Nickel-Zinc, and Copper-Zinc solid solutions. Potentiodynamic corrosion tests demonstrated a significant improvement in corrosion resistance, with copper-alloyed samples exhibiting at least three times the resistance of the base alloy.

[0216] These findings highlight the potential of this surface alloying method to extend the lifespan of brass components, reduce element leaching into water systems, and provide a targeted, scalable solution for corrosion-prone areas in industrial applications.Example 4: Low-Cost Surface Alloying of Copper Alloys Including Brass to Improve Corrosion Resistance in Chlorine and Chloramine Rich Environments

[0217] This work aims to develop the technology of low-cost surface alloying of copper alloy plumbing fixtures during sand casting, to extend the life of components and reduce corrosion and surface damage in water containing chlorine and chloramine.

[0218] The inventors have been able to demonstrate the feasibility of surface alloying of two copper alloys, including yellow brass and Bi-alloy, at the lab scale; slurries containing metal powders were coated on the selected surfaces of molds and cores to achieve surface alloying on inner and outer surfaces of castings. Limited castings have also been made on the industry floor with slurry-coated molds and cores. However, the surface alloyed layers observed in early stage, lab-cast samples were thin (<200 μm) and often had defects and nonuniformities.

[0219] The methods disclosed herein are much cheaper and does not require line of sight as in laser surface alloying and other surface alloying processes; it is also especially suited for surface alloying interior surfaces of castings by coating the slurry on cores that form the internal surfaces. In fact, our process can enable varying degrees of surface alloying on different surfaces of the same casting depending on different exposures to corrosive environments. In addition, the methods disclosed herein enable the use of lower-cost copper alloys in the interior with surface alloyed layers instead of using highly alloyed castings where costly and scarce alloying elements are incorporated throughout the cross sections.

[0220] The inventors' process can be readily implemented by either captive foundries or at foundries that manufacture plumbing castings of copper alloys by coating the surfaces of molds and cores with slurries containing metal powders before pouring the melts in the molds. The inventors will provide the know-how on the selection of metal or alloy powders to be mixed in slurries and the application of slurries on selected surfaces of molds and cores. In addition, the use of surface alloyed components will reduce the amount of metal ions leaching into the water, reducing dezincification and pit formation on the casting surface. For example, enriching the surface of yellow brass in Cu will bring the surface composition closer to red brass, which has higher corrosion resistance. Enriching the surface of red brass with Ni and other elements will further increase their corrosion resistance, which shows much higher life in chloramine environments, at much lower costs. The work aims to improve the corrosion resistance of copper alloys, including brass, in water systems that have chlorine and chloramine. Brass, commonly used in tubing, piping, faucets, and valves, is prone to corrosion and dezincification from free chlorine, including chloramine-derived chlorine. The feasibility of surface alloying of yellow brass and Bi-alloy by sand casting process has been demonstrated on a lab scale where thin surface alloyed layers (<200 μm) were produced on yellow brass and bi-alloy castings; we also were able to demonstrate that castings can be poured with slurry coated on molds and cores in industrial conditions.

[0221] The objective of this work is to improve the surface alloying process to control the thickness, soundness, uniformity, reproducibility, and composition of the surface alloyed layer. The corrosion resistance and material characteristics of the surface-alloyed samples will be compared against standard alloys (yellow brass, red brass, bi-alloy) to determine the effectiveness of the surface alloying process for increasing corrosion resistance. Selected prototypes of plumbing components will be cast on the industry floor, and their enhanced life will be demonstrated in lab-scale corrosion tests and, if possible, under actual service use. Additionally, a techno-economic analysis will be done after optimization of the process to demonstrate the cost savings by using surface alloyed castings with enhanced corrosion resistance, compared to base alloy castings and through alloyed castings.Objectives:1. Control of thickness, uniformity, soundness, reproducibility, and composition of the surface-alloyed layers both in samples and prototypes cast.

[0223] 2. Molds and Cores for selected castings will be coated with powder slurries to produce surface alloyed prototype castings.

[0224] 3. Demonstrate the improvement in corrosion resistance of surface alloyed castings in chlorine and chloramine-rich environments, including resistance to dezincification and pitting.

[0225] 4. Benchmark galvanic corrosion potential of surface alloyed samples to standard commercially-available alloys (recreate galvanic series and incorporate our SA samples)

[0226] Others observed that brass faucets exhibited three times greater durability in the absence of chloramine in water compared to water containing 1 mg / l of chloramine. Earlier work theorized that corrosion is initiated with a direct oxidative attack of the copper surface by free chlorine, followed by the dissolution of the oxidative products from the surface.

[0227] Surface alloying is a surface engineering technique where the outer layer of base material is intentionally enriched in selected alloying elements to a depth of tens to thousands of microns. Methods like carburizing, nitriding, chromizing, and boronizing have been commonly used for surface alloying of steels to enhance specific material properties such as wear and corrosion resistance. Various other surface alloying techniques, including diffusion coating, laser surface alloying, friction stir processing, and electron beam melting, have been explored by researchers for surface alloying. Others' surface-alloyed Brass surface with a Ni—Cr—Si—B powder using a high-power laser, resulting in improved corrosion and erosion resistance. However, these methods are expensive, difficult to scale up, require direct line-of-sight, and often require additional post-processing, leading to increased manufacturing time and costs. The approach disclosed here integrates surface alloying directly into the conventional sand-casting process, with only one additional step of coating the molds and / or cores with a slurry containing alloying elements before pouring the melt into the mold.

[0228] Increasing the weight percentage of certain alloying elements on the surfaces of copper alloy castings will increase their corrosion resistance. For instance, others' high in Ni components lasted 330 days in water containing chloramine, whereas components of red brass and yellow brass lasted 63 days and 14 days respectively, documenting that adding Nickel, Copper and other elements to the surface of these castings, will improve their corrosion resistance. This disclosed research focuses on increasing copper in the surface of yellow brass components, resulting in a composition closer to red brass on the surface while containing yellow brass in the interior bulk. Yellow brass is more susceptible to dezincification due to its higher Zinc content, leading to material degradation, especially in chloride-rich environments. Likewise, the surfaces of red brass and Bi-Alloy, and other alloy castings will be enriched in Ni and other elements to further improve their corrosion resistance.Results

[0229] In initial experiments, commercial binders were used to make slurries for coating molds and cores. Powders of Cu, Ni, Al, and Sn were added to the slurry. The SEM / EDS result, (FIGS. 14(a) and 14(b), shows the microstructure of sample S9, bi-alloy poured in a mold coated with a slurry containing Ni powders, and its EDS analysis showing the change in composition from the surface alloyed layer to base metal (showing enrichment in Ni). Similar results are shown in FIGS. 14(c) and 14(d), where the surface of yellow brass samples was enriched with Cu. FIG. 15(a) shows the samples cast. FIGS. 15(b) and 15(c) show the slurry-coated cores placed in molds and the castings made using this setup, respectively. In some cases, the surface alloyed layers showed porosity and non-uniform thickness etc.

[0230] Contemplated variables including the type of binders; powder sizes and shapes; slurry consistency, and processing parameters, were optimized to increase the thickness, soundness, and uniformity of surface alloyed layers. Quantitative relationships were developed between processing variables and these parameters. Copper alloys, including yellow brass and Bi-alloys were cast.

[0231] The corrosion resistance of surface alloyed layers on both coupons and selected prototypes will be tested using linear polarization, potentiodynamic tests and immersion in mediums containing chlorine and chloramine. The life of surface alloyed components and samples, and corrosion rates, will be tested. Additional tests will be done with both SA and commercial alloys to benchmark the galvanic potential in salt water. This will provide a simple comparative rating using the standard galvanic series as a reference.

[0232] Further contemplated factors:

[0233] 1. The transfer mechanism of alloying elements from the slurry-coated molds and cores to the surface alloyed layer and the solidification of material in the surface alloyed layer will be analyzed. The composition, soundness, reproducibility, thickness, and uniformity of surface alloyed layers enriched in Cu, Ni, Sn, and Al and their combinations will be optimized.

[0234] 2. Corrosion testing samples and prototype castings made in the industry will be done. Dezincification and pitting during corrosion tests will be studied in addition to mass loss from the surface. Prototype surface alloyed samples will be benchmarked to commercial alloys by recreating the galvanic series via corrosion potential measurements in salt water.

[0235] 3. The increase in the life of components as a result of surface alloying will be quantified, and the ability to predict the life of surface alloyed castings will be developed.

[0236] 4. Prototypes will be cast using coated cores for surface alloying of internal surfaces, using bi-alloy and other copper alloys.

[0237] 5. Prototypes will be cast using coated molds for surface alloying of external surfaces using yellow brass.

[0238] 6. Techno-economic analysis of cost savings and increase in profitability as a result of surface alloying technology.Example 5: Surface Alloying of BrassMaterials and Methods

[0239] A total of 64 cores were received and were divided in the format shown in Table 8. Step 1 was to coat all cores with a graphite wash to prevent any reaction between the melt and sand particles. This is a standard practice in the industry. Following the graphite wash, all cores were then manually coated with the corresponding slurry mixtures. Afterward, the coated cores were dried at ambient temperature. This drying process is necessary to ensure the volatile compounds are evaporated before the casting process. This further helps to reduce the formation of porosities. Once dried, the cores were transferred back to the Fall River Foundry and molten metal was poured in the molds containing the cores to make the casting.TABLE 8Copper alloy specimens cast. L = low, H = high, U = uncoated, N = Nickel coated, P = polyvinyl alcohol (PVA), S = superplasticizerSamplewt % ofReinforcementNi-No.BiAl2O3SiCGraphiteBinderReinforcement(g)Cu(g)1LP0.0150.31682.5,2.52LP0.0150.31682.5,2.53LP0.0150.31682.5,2.54LP0.0150.31682.5,2.55LS0.0150.31682.5,2.56LS0.0150.31682.5,2.57LS0.0150.31682.5,2.58LS0.0150.31682.5,2.59HP0.030.63362.5,2.510HP0.030.63362.5,2.511HP0.030.63362.5,2.512HP0.030.63362.5,2.513HS0.030.63362.5,2.514HS0.030.63362.5,2.515HS0.030.63362.5,2.516HS0.030.63362.5,2.517UP0.153.1682.5,2.518UP0.153.1682.5,2.519UP0.153.1682.5,2.520UP0.153.1682.5,2.521US0.153.1682.5,2.522US0.153.1682.5,2.523US0.153.1682.5,2.524US0.153.1682.5,2.525NP0.153.1682.5,2.526NP0.153.1682.5,2.527NP0.153.1682.5,2.528NP0.153.1682.5,2.529NS0.153.1682.5,2.530NS0.153.1682.5,2.531NS0.153.1682.5,2.532NS0.153.1682.5,2.533UP0.153.1682.5,2.534UP0.153.1682.5,2.535UP0.153.1682.5,2.536UP0.153.1682.5,2.537US0.153.1682.5,2.538US0.153.1682.5,2.539US0.153.1682.5,2.540US0.153.1682.5,2.541NP0.153.1682.5,2.542NP0.153.1682.5,2.543NP0.153.1682.5,2.544NP0.153.1682.5,2.545NS0.153.1682.5,2.546NS0.153.1682.5,2.547NS0.153.1682.5,2.548NS0.153.1682.5,2.549UP0.153.1682.5,2.550UP0.153.1682.5,2.551UP0.153.1682.5,2.552UP0.153.1682.5,2.553US0.153.1682.5,2.554US0.153.1682.5,2.555US0.153.1682.5,2.556US0.153.1682.5,2.557NP0.153.1682.5,2.558NP0.153.1682.5,2.559NP0.153.1682.5,2.560NP0.153.1682.5,2.561NS0.153.1682.5,2.562NS0.153.1682.5,2.563NS0.153.1682.5,2.564NS0.153.1682.5,2.5Copper alloy specimens cast. L = low, H = high, U = uncoated, N = Nickelcoated, P = polyvinyl alcohol (PVA), S = superplasticizerSurfaceDesiredLocalLocalNi-SampleAreaThicknessVolumeMasswt % ofReinforcementCuNo.(cm2)(cm)(cm3)(grams)Reinforcement(g)(g)1240.12.421.120.0150.31685, 52240.12.421.120.0150.31685, 53240.12.421.120.0150.31685, 54240.12.421.120.0150.31685, 55240.12.421.120.0150.31685, 56240.12.421.120.0150.31685, 57240.12.421.120.0150.31685, 58240.12.421.120.0150.31685, 59240.12.421.120.030.63365, 510240.12.421.120.030.63365, 511240.12.421.120.030.63365, 512240.12.421.120.030.63365, 513240.12.421.120.030.63365, 514240.12.421.120.030.63365, 515240.12.421.120.030.63365, 516240.12.421.120.030.63365, 517240.12.421.120.153.1685, 518240.12.421.120.153.1685, 519240.12.421.120.153.1685, 520240.12.421.120.153.1685, 521240.12.421.120.153.1685, 522240.12.421.120.153.1685, 523240.12.421.120.153.1685, 524240.12.421.120.153.1685, 525240.12.421.120.153.1685, 526240.12.421.120.153.1685, 527240.12.421.120.153.1685, 528240.12.421.120.153.1685, 529240.12.421.120.153.1685, 530240.12.421.120.153.1685, 531240.12.421.120.153.1685, 532240.12.421.120.153.1685, 533240.12.421.120.153.1685, 534240.12.421.120.153.1685, 535240.12.421.120.153.1685, 536240.12.421.120.153.1685, 537240.12.421.120.153.1685, 538240.12.421.120.153.1685, 539240.12.421.120.153.1685, 540240.12.421.120.153.1685, 541240.12.421.120.153.1685, 542240.12.421.120.153.1685, 543240.12.421.120.153.1685, 544240.12.421.120.153.1685, 545240.12.421.120.153.1685, 546240.12.421.120.153.1685, 547240.12.421.120.153.1685, 548240.12.421.120.153.1685, 549240.12.421.120.153.1685, 550240.12.421.120.153.1685, 551240.12.421.120.153.1685, 552240.12.421.120.153.1685, 553240.12.421.120.153.1685, 554240.12.421.120.153.1685, 555240.12.421.120.153.1685, 556240.12.421.120.153.1685, 557240.12.421.120.153.1685, 558240.12.421.120.153.1685, 559240.12.421.120.153.1685, 560240.12.421.120.153.1685, 561240.12.421.120.153.1685, 562240.12.421.120.153.1685, 563240.12.421.120.153.1685, 564240.12.421.120.153.1685, 5Results and DiscussionOptical Microscopy

[0240] FIG. 16 presents the sample numbers against the highest thickness of the surface-alloyed layer achieved for each specimen cast using the in-mold surface alloying approach. It is evident that the surface-alloyed specimens with Ni-coated SiC, samples 41-48, achieved the thickest surface composited layers. Additionally, the group of castings with Ni-coated SiC proved to be the most successful, with 6 out of 8 samples achieving successful surface compositing. In contrast, the surface-alloyed samples 17-24, with uncoated Al2O3 were unsuccessful, showing no evidence of measurable surface alloy layer formation. A similar trend was observed for uncoated SiC and uncoated graphite samples where no measurable surface composited layer was observed under conditions of present manufacture. The present work indicates that nickel coating facilitates the transfer of graphite and ceramic particles from the slurry to the surface composited layer. It appears that uncoated ceramic particles will require modification in melt composition or pretreatment for them to form a surface composited layer.

[0241] FIG. 17 shows the optical microstructure of all successful samples cast in Fall River, along with their corresponding sample numbers. The depth of surface alloying for all samples has been marked on the micrographs. The greatest thickness of surface alloyed or surface composited layer was observed in sample 44, with a 1190 μm surface-alloyed layer produced using Ni-coated SiC mixed with a PVA binder. It appears that using this PVA as a binder results in better surface-alloyed layers.

[0242] Table 9 presents the quantitative measurements of consistency and porosity of surface-alloying layers and base metal. Based on the data from Table 9 and FIG. 16, the optimal samples in terms of surface-alloying layer thickness, consistency, and low porosity are Samples 41-48, where the cores were coated with Ni-coated SiC. Samples with the highest consistency are indicated in red font. The samples fabricated with superplasticizer achieved the highest thickness of surface alloying, making them superior in terms of alloy layer formation.

[0243] Among these samples, Sample 47 exhibits high consistency and low porosity in both the surface-alloyed or surface composited layer and the base metal, making it an excellent specimen. This result is likely due to the presence of a Ni coating on the graphite layers, which enhances wettability between the molten metal and the slurry. The Ni—Cu phase diagram (FIG. 18) demonstrates the high solubility of Ni in Cu.TABLE 9Quantitative measurements of consistencyof surface alloying layers.Porosity level in Brass Samples 2025SampleSurface alloyednumberConsistency levellayerBase metal1LOWHIGHLOW3LOWHIGHLOW5LOWMEDIUMLOW6MEDIUMMEDIUMLOW7HIGHMEDIUMLOW9LOWHIGHMEDIUM10HIGHMEDIUMLOW11HIGHHIGHHIGH12MEDIUMHIGHLOW15LOWLOWLOW25HIGHLOWMEDIUM26MEDIUMLOWLOW28LOWLOWLOW30MEDIUMLOWLOW31HIGHLOWLOW32LOWLOWLOW41LOWLOWHIGH42MEDIUMMEDIUMHIGH43MEDIUMLOWMEDIUM44HIGHMEDIUMLOW47HIGHLOWLOW48MEDIUMLOWLOW57HIGHMEDIUMMEDIUM58HIGHMEDIUMLOW59HIGHMEDIUMLOW60HIGHMEDIUMHIGH62LOWLOWLOWScanning Electron Microscopy (SEM)

[0244] FIG. 19 shows the scanning electron microscopy (SEM) image of a portion of the surface-alloyed layer of Sample 47. This sample exhibits a surface-composited layer with a homogeneous distribution of Si and Ni. The coating is separated from the surface-alloyed layer by a dashed line.

[0245] Comparing uncoated particle-reinforced surface composite vs coated particle-reinforced surface composites:

[0246] Sample 47 was selected as the optimal Ni-coated particle-reinforced surface composite sample. However, none of the uncoated particle-reinforced surface composited showed measurable amount of ceramic particles in the surfaces (FIG. 16). Among them, samples with a high bismuth content exhibited acceptable consistency with medium level of porosity in the surface-alloyed layer. Table 10 presents a comparison of the highest achieved surface-alloyed layer thickness between Sample 47 and Sample 10.TABLE 10A comparison between of the highest achieved surface-alloyedlayer thickness between Sample 47 and Sample 10.Sample'sHighestConsistencyPorosity level innumberthickness (um)levelcoated layer47818.9HighLow10518.1HighMediumExample 6: Low-Cost Surface Alloying of Yellow Brass to Improve Corrosion Resistance in Chlorine and Chloramine-Rich EnvironmentsTABLE 11Elemental Composition of yellow brass.ElementCuZnAverage (wt %)6040TABLE 12Life of various alloys in chloramine-rich water.AlloyComponent life in chloramineYellow Brass32 daysRed Brass63 daysMonel330 days TABLE 13Elemental composition of Bi-Alloy Brass.ElementCuSnPbZnFeNiAlSiSbSPSeBiMnAverage89.14.460.0204.610.0560.8250.0030.000.0440.0070.0250.0081.700.00(wt %)TABLE 14Elemental composition of Monel 400.ElementCuFeCSiSMnNiMin (wt %)28—————BalanceMax (wt %)342.50.30.50.0242BalanceTABLE 15Alloying powders utilized for the process.Alloying ElementParticle SizePurityCu−200 mesh99%Ni−100 mesh99.9%  Cu—Sn (90 wt %-10 wt %)−200 mesh99%Al 200 mesh99%TABLE 16List of successful experiments conducted.PouringTemper-Sam-AlloyingaturepleElement(C.)AlloyTypeFluxBinderS7Ni>1200Bi-AlloyOpen PourBoraxSodiumPolyacrylateS9Ni>1200Bi-AlloyOpen PourBoraxModifiedRefcobar1010S11Ni>1250Bi-AlloyOpen PourBoraxModifiedRefcobar1010S18Ni1200Bi-AlloyOpen PourBoraxModifiedRefcobar1010S19Ni1100Bi-AlloyOpen PourBoraxModifiedRefcobar1010S20Ni1100Bi-AlloyOpen PourNoModifiedRefcobar1010S27Ni-Al1200YellowOpen PourGlass ModifiedBrassand Vibrantz BoraxTechnologiesS29Cu-Al1200YellowOpen PourGlass ModifiedBrassand Vibrantz BoraxTechnologiesTABLE 17List of samples using yellow brass.SampleAlloying ElementsRatioBinderC0———Modified VibrantzC1Cu——TechnologiesC2Ni——C3CuAl1:1C4NiAl1:1C5Al——C6CuSn9:1C7CuNi1:1C8CuAl3:1C9NiAl3:1C10CuNi3:1TABLE 18List of samples using Bi-Alloy brass.SampleAlloying ElementsRatioBinderB1Cu——Modified RefcobarB2Cu——1010B3Ni——B4Ni——B5CuAl1:1B6CuAl1:1B7CuAl3:1B8CuAl3:1B9NiAl1:1B10NiAl1:1B11NiAl3:1B12NiAl3:1B13Al——B14Al——B15CuSn9:1B16CuSn9:1B17CuNi3:1B18CuNi3:1B19CuNi4:1B20CuNi4:1TABLE 19List of samples made using Bi-Alloy brass.SampleAlloying ElementsRatioBinderO1Cu——Modified VibrantzO2Cu——TechnologiesO3Ni——O4Ni——O5CuAl1:1O6CuAl1:1O7CuAl3:1O8CuAl3:1O9NiAl1:1O10NiAl1:1O11NiAl3:1O12NiAl3:1O13Al——O14Al——O15CuSn9:1O16CuSn9:1O17CuNi3:1O18CuNi3:1O19CuNi4:1O20CuNi4:1TABLE 20List of samples made using Bi-Alloy brassUWMNotationAlloying ElementsRatioBinderNickel-Graphite TrialsP1NiGraphite1:1Modified VibrantzTechnologiesP2NiGraphite1:1Modified Refcobar 1010Sprinkle Trials*P3Ni——Modified VibrantzTechnologiesP4Ni——Modified Refcobar 1010P5CuSn9:1Modified VibrantzTechnologiesP6CuSn9:1Modified Refcobar 1010Control SamplesP7————P8————Extra SamplesP9CuNi1:1Modified VibrantzTechnologiesP10ACu——Modified Refcobar 1010P10BAl——Modified VibrantzTechnologies*Sprinkle Trials: A layer of binder was applied on the core surface, following which alloying powder was sprinkled on the binder. This methodology was implemented to determine whether the alloying powders being mixed with the binder vs. sitting on top of the binder will have any effect on the surface alloyed layer produced.Sample Observations:Sample S9 of Table 16 and FIG. 20-21: The mold was chemically bonded sand. A larger melt volume was used. A distinct surface alloy (SA) layer was observed. There is consistent Ni % in the SA layer. The SA has a uniform thickness. Some porosity was observed still in the cast.TABLE 21Chemical composition of the bulk metal and surface alloyed layerof Sample S9, corresponding to spectrum locations FIG. 22.CNiCuZnSnSpectrum(% wt)(% wt)(% wt)(% wt)(% wt)Spectrum 1 (SA layer)24.2654.2317.364.14Spectrum 2 (SA layer)2.1825.6363.154.025.02Spectrum 3 (bulk)3.8787.923.664.84Spectrum 4 (bulk)4.7690.714.53Sample S18 of Table 16 and FIG. 23: The mold was chemically bonded sand. A continuous SA layer was observed. Ni % in the SA layer was above 20 wt %. Porosity was detected in the casting.TABLE 22Chemical composition of the bulk metal and surfacealloyed layer of Sample S18, correspondingto spectrum locations shown in FIG. 23.NiCuZnSnSpectrum(% wt)(% wt)(% wt)(% wt)Spectrum 1 (SA layer)21.8671.153.003.98Spectrum 2 (SA layer)28.2664.123.584.03Spectrum 3 (bulk)1.6589.473.964.92Spectrum 4 (bulk)1.8189.714.493.98Sample S19 of Table 16: The mold was chemically bonded sand. A very thin surface alloy layer of about 15 μm to about 20 μm was observed. The SA layer was continuous. The Ni % in the SA layer was above 20 wt %. Low porosity was observed in the casting.TABLE 23Chemical composition of the bulk metal and surfacealloyed layer of Sample S19, as shown in FIG. 24.SpectrumNi (% wt)Cu (% wt)Zn (% wt)Sn (% wt)Spectrum 1 (SA layer)48.7812.530.0038.69Spectrum 2 (SA layer)28.5965.411.314.69Spectrum 3 (bulk)1.2492.092.214.46Spectrum 4 (bulk)0.8492.411.804.95Sample S27 of Table 16: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. The Cu % in the SA layer was above 88.45 wt %. No porosity was observed in the casting.TABLE 24Chemical composition of the surface alloyed layer of Sample S27collected at a range of locations in the surface alloy layer.AlCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer, surface-1.4888.4510.07most)Spectrum 2 (SA layer, mid-0.6471.1128.25layer)Spectrum 3 (SA layer, closest0.4163.6235.97to base metal)Sample S27 of Table 16: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. The Cu % in the SA layer was above 80 wt %. No porosity was observed in the casting.TABLE 25Chemical composition of surface alloyed layer of Sample S27collected at a range of locations in the surface alloy layer.AlCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer, surface-0.8190.478.10most)Spectrum 2 (SA layer, mid-1.0469.3628.37layer)Spectrum 3 (SA layer, closest0.0066.0833.43to base metal)Sample C4 of Table 17: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm to about 75 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample C10 of Table 17: The mold was chemically bonded sand. A thin surface alloy layer of about 25 μm to about 50 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B4 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 26Chemical composition of the bulk metaland surface alloyed layer of Sample B4.NiCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer)62.1434.483.38Spectrum 2 (Base Metal)1.0494.404.56Sample B2 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm to about 120 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B3 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 150 μm was observed. The SA layer was discontinuous. Some porosity was observed in the casting.Sample B7 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 75 μm to about 90 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B10 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample P3 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm to about 200 μm was observed. The SA layer was discontinuous. Minor porosity was observed in the casting.Sample P5 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm was observed. The SA layer was discontinuous. Minor porosity was observed in the casting.Sample P9 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 200 μm to about 350 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 27Chemical composition of the bulk metaland surface alloyed layer of Sample P9.NiCuSnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer)36.6457.026.34Spectrum 2 (SA layer)18.9177.603.49Spectrum 3 (Bulk)—93.626.38Spectrum 4 (Bulk)—95.914.09Example 7: Select Corrosion Testing ResultsSample P9 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 200 μm to about 350 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 28Potentiodynamic corrosion testing results for Bi-alloy base,Sample 22, Sample 28, and Sample P9 (49). A 1 cm2 areawas tested. Each test was duplicated. Counter electrode:Platinum mesh. Reference electrode: Ag / AgCl in 3.5M KCl.Electrolyte: Tap water with about 2 ppm chloramine.SA AlloyingSampleelementE corr (mV vs Ref)I corr (μA)Bi-alloy base1090.714Sample 22Cu950.220Sample 28Cu:Al = 3:1720.227Sample P9 (49)Cu:Ni = 1:1670.249Samples having a surface alloy layer demonstrated about 3× more corrosion resistance than the bi-alloy base.Example 8: Surface Alloying and Surface Compositing of Copper Alloy Castings Using Mold and Core CoatingsThis work presents a technique for simultaneous surface alloying and surface compositing (SASC) of C89836 brass castings. Core surfaces were coated with a slurry of Cu, Ni, and Ni-coated graphite powders before casting. During solidification, Ni and Cu dissolved into the melt and enriched the surface, while graphite particles were embedded in the matrix, forming a composite layer. Microstructural characterization by optical microscopy, SEM, and XRD confirmed uniform Ni enrichment and graphite incorporation. Electrochemical and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) tests showed SASC castings had reduced corrosion rates and lower lead leaching, while machinability improved through the formation of short, granular chips instead of long, spiral chips. Compared with both the base alloy and Ni / Cu surface alloyed castings, SASC provided simultaneous improvements in corrosion resistance, lead leaching mitigation, and machinability. These findings demonstrate the potential of SASC technique for producing safer, high-performance brass components by integrating alloying and compositing in a single step.Introduction

[0265] Surface alloying modifies the surface of a base alloy by adding elements such as C, Ni, or Cr to improve wear, hardness, or corrosion resistance. It modifies surface composition and properties near the surface without altering the bulk casting, offering a cost-effective way to enhance performance by selectively alloying surface layers and reducing the need for expensive alloying elements. Surface-alloyed components are used in automotive, aerospace, tooling, and water industry applications. For brass components, surface alloying with Ni, Cr, and B using lasers has shown improvement in corrosion resistance; however, laser processing is costly and requires direct line-of-sight. Researchers have also explored diffusion coating, friction stir processing, and electron beam melting for surface alloying.

[0266] Surface alloying can be commercially valuable for brass used in water systems because it prolongs component life, reduces maintenance costs, and ensures compliance with water safety regulations. Early studies linked chloramine in water to accelerated impingement attack and cavitation; others showed that brass faucets lasted three times longer without chloramine exposure. Copper corrosion is strongly pH-dependent, with higher pH reducing chlorine-induced leaching. Later work suggested corrosion begins with oxidative attack by free chlorine, followed by dissolution of products, and is promoted by higher ionic strength, inorganic carbon, and temperature. Diffusion within oxide films slows overall corrosion. Alloying throughout the cross-section, as in Monel or red brass, show superior water-corrosion resistance compared with yellow brass.

[0267] A prominent corrosion mechanism in brass is dezincification, which involves the selective removal of Zn from the alloy surface exposed to the corrosive medium, resulting in a porous copper structure. This process occurs as Zn is more reactive than Cu and is more easily oxidized and dissolved in water, especially in the presence of slightly acidic or basic conditions. To prevent dezincification in brass alloys, additions of inhibitors like Arsenic (As) and Tin (Sn) have been used. Arsenic reduces Cu ions to form a protective cuprous oxide layer, while tin creates a film at grain boundaries to inhibit zinc diffusion. Using brass with lower Zn content or applying protective coatings can also help mitigate these corrosion processes. In chloride solutions at 68 F (20 C), α-brasses are prone to dezincification, particularly in stagnant areas and at elevated temperatures, even under flowing conditions. Dezincification is most severe in (α+β) and β-brasses. Brasses containing less than 30 wt % Zn predominantly form the α-phase and thus exhibit greater resistance to dezincification. Taps of red brasses and Monel alloys have shown much longer life than yellow brasses, suggesting that higher Ni and Cu contents reduce corrosion.

[0268] Leaching in brass alloys often involves the release of Pb and Cu into water, particularly in soft, corrosive conditions. Leaching is most pronounced during the first 24 hours of water stagnation, and regular flushing is an effective way to reduce metal concentrations. Adjusting the pH to around 7.5 or higher, maintaining sufficient alkalinity, and using orthophosphate as a corrosion inhibitor can further reduce lead and copper leaching by forming protective layers on the metal surfaces.

[0269] Lead has traditionally been added to brass to improve machinability by forming discrete particles that act as solid lubricants, resulting in smaller chips, smoother surface finish, and reduced tool wear. However, due to its toxicity and environmental impact, its use in pipes and fittings has been heavily restricted, and the U.S. Environmental Protection Agency (EPA) lowered the action level for lead in drinking water from 0.05 mg / L to 0.015 mg / L in 1991. These regulations have driven the development of lead-free brass alloys with acceptable machinability. Although lead decreases the corrosion rate of brass and reduces susceptibility to dezincification, shifting the breakdown potential to more noble values, its health risks outweigh these benefits. Lead levels in drinking water are closely monitored, and exceeding the 15-ppb action level under the EPA's Lead and Copper Rule requires corrective actions. In cases where no lead is added to copper alloys as an alloying element, there is residual Pb in alloys made from scrap, and this residual Pb can leach out when the cast components are in contact with water.

[0270] Bismuth, although not as toxic as lead, has been shown to be as effective as lead in improving machinability. This element is also non-soluble in brass alloys and has a relatively low melting point. However, the availability of Bi is limited, and its cost is much higher than that of Pb. Bi also segregates the grain boundaries, which causes an increase in the brittleness of the casting.

[0271] Incorporation of graphite in Cu alloy matrices has been reported in the literature using powder metallurgy techniques and, to a limited extent, using the stir casting technique. Graphite particles in Cu alloy matrix using a stir mixing process in the melt, where the graphite particles were intended to replace Pb for machinability purposes. In earlier work, graphite particles were incorporated throughout the cross-section of yellow brasses by stir mixing graphite and Ti in the entire melt, followed by casting. In these studies, the incorporation of graphite in the Cu alloys showed improvement in machinability, similar to the improvement in machinability achieved by additions of Pb. Additionally, the incorporation of graphite particles did not decrease the corrosion resistance of the Cu alloys. The present work improves upon prior work in that it eliminates the need to disperse graphite particles throughout the melt and throughout the castings, which is associated with nonuniform distribution of graphite in the melt and problems of graphite flotation in the melt and nonuniform distribution of graphite in slowly solidified castings. In the present work, these graphite particles are incorporated only near the surface, where they are intended to aid machining, reduce leaching, and improve corrosion resistance. The amount of graphite needed in SASC castings is significantly smaller compared to the case when graphite is incorporated throughout the cross-section of the castings.

[0272] The incorporation of graphite particles in copper alloys using powder metallurgy and stir casting have shown to improve wear resistance and machinability of copper alloys. However, powder metallurgy techniques are expensive and not suitable for producing plumbing components. Stir casting has been successfully used to incorporate graphite particles throughout the cross section of castings; the incorporation of graphite particles led to improvement in machinability of castings, similar to lead, improvement in wear resistance and has no measurable effect on corrosion rate. However, there were problems associated with achieving a uniform distribution of graphite in sand-cast copper alloy castings due to the flotation of particles.

[0273] Disclosed herein is a technique of surface alloying and surface compositing of copper alloy sand castings is described. The technique involves coating the molds or cores with slurry containing metal powders like Ni and Cu (for surface alloying) and Ni-coated graphite particles (for surface compositing). The casting surfaces in contact with the slurry when molten metal is poured into the mold are enriched in Ni and Cu (Surface Alloying), and in surface compositing, incorporate graphite particles near the surface when Ni-coated graphite particles are present in the slurry. The microstructure, chemical composition, and phases present in the surface alloyed and surface composited layers have been characterized, and improvements in corrosion resistance, machinability, and reduction of leaching of lead have been demonstrated. This technique represents an improvement over stir mixing and casting since graphite, Ni, and Cu are incorporated only near the surface, where they are needed for corrosion and leaching resistance and for machinability, thus reducing the amounts of Ni, Cu, and graphite needed in through-alloyed and through-composited castings. The surface alloying and surface compositing technique can be easily adopted for sand-cast copper alloy components.Materials and Methods

[0274] A total of eight sand cores were coated with slurries containing metal powders and Ni-Graphite powders at the University of Wisconsin-Milwaukee (UWM) and subsequently cast at a partner foundry. Each core was first coated with two layers of HA International Technikoat, a graphite-based mold and core wash designed to minimize reactions between molten metal and core sand, and then allowed to dry under ambient conditions for 24 hours. Following this, the cores were coated with a slurry containing Ni and Cu powders, graphite particles, and one of two water-based binders: polyvinyl alcohol (PVA) or a combination of PVA and a superplasticizer, in certain cases. Ni was incorporated specifically to improve the corrosion resistance and reduce leaching of the Bi-Alloy brass.

[0275] The slurry preparation process was a factor for achieving the desired surface alloying properties. C89836 brass (87-91 wt % Cu) was used as the base alloy, and Ni was selected as the alloying element to facilitate surface alloying. Incorporating Ni is expected to improve the corrosion resistance in the surface alloyed-surface composited (SASC) layer. The composition of the C89836 is shown in Table 2 and the composition of the slurries applied on the core surfaces is shown in Table 29 and Table 30.

[0276] The binder was prepared by dissolving the PVA powder in water at 176 F (80 C) to form a 10 wt % solution. The metal powders (Ni and Cu) and Ni-coated graphite particles were measured in quantities shown in Table 3, and the binder was added while maintaining a constant stirring rate. The viscosity of the slurry binder was important since low viscosity would lead to the separation of the powders. The slurry containing metal powders and Ni-coated graphite powders was applied on the surface of the cores to form a coating. The cores were then dried at room temperature for 48 hours, with no external heat applied during this process. The casting process has been schematically shown in FIG. 2, showing the application of the slurry on a sand core, followed by the pouring of the melt.TABLE 29Surface composite samples cast.SampleAlloyingGraphiteNoPowdersPowderBinder1-4Ni—CuNi-coatedPVA(1:1)Graphite5-8Ni—CuNi-coatedPVA + Superplasticizer(1:1)Graphite(SP)TABLE 30Composition of the Ni and Cu powders and Ni-coated graphiteparticles utilized to form the slurry for coating the coresSampleBinderNi-Graphite (g)Ni Powder (g)Cu Powder (g)Total Powder (g)1PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)2PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)3PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)4PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)5PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)6PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)7PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)8PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)9PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)Following casting in sand molds, the castings were sectioned from the surface alloyed-surface composited (SASC) regions for metallographic characterization. Samples were cut using a bandsaw, mounted in conductive phenolic resin, and ground sequentially with SiC abrasive papers of 180, 320, 600, 800, and 1200 grit. Final polishing was performed with 1 μm alumina suspension followed by 0.05 μm colloidal silica to obtain a mirror finish. Residual polishing media were removed using water and isopropyl alcohol. The polished samples were etched with Copper No. 2 (a ferric chloride-based etchant) to reveal the microstructure. Optical microscopy was conducted using a Nikon EPIPHOT 300 microscope under polarized light, while microstructural features were further examined with a JEOL 6460LV scanning electron microscope (SEM) using backscattered (BSE) and secondary electron (SE) imaging. Phase identification was conducted via X-ray diffraction (XRD) using a Bruker D8 Discover system was equipped with a Ni filter and Cu target and operated at 40 kV and 40 mA. The machinability test was performed using a sweeping tool with a depth profile of 0.635 mm ( 1 / 100th of an inch) on the samples to evaluate the chip formation behavior.

[0278] A potentiodynamic polarization test was performed to characterize the corrosion resistance of the samples. A potentiostat, SP-200 BioLogic, was used to run the corrosion test. The electrolyte used for the corrosion test was tap water, with an estimated chloramine concentration of ~2 ppm. The SASC samples and platinum wire mesh were used as the working electrodes and counter electrode, respectively, while Ag / AgCl was used as the reference electrode. The lead leaching tests were performed using a modified method of the NSF-61 testing method. As the samples only had one surface that was surface alloyed or surface composited, a borosilicate glass tube, open from both ends, was fixed on the surface alloyed and / or surface composited region using a binding medium. The tube was then filled with 30 ml of leaching liquid, which was tap water in this study, to initiate the test. As tap water contains chlorine or chloramine, the subsequent corrosion and leaching occurred from the sample surface. The test was conducted for a period of 24 hours at room temperature, following which the water in contact with surfaces was collected. The concentration of lead was quantified using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in the range of ppb. The base alloy, C89836, with a maximum lead concentration of 0.25 wt %, as well as a surface alloyed-surface composited sample (Ni—Cu-Graphite), were the samples tested in this study, along with two control samples of DI water and tap water.Results and Discussion

[0279] FIG. 26 shows the optical micrograph of a C89836 brass casting prepared using Ni—Cu powder and Ni-coated particles with a PVA binder in the slurry, which was coated on the cores. The micrographs show graphite particles that appear as dark particles dispersed in the surface layer. FIGS. 26(a) and 26(b) show that the SASC layer contains Ni-rich regions appearing as islands. FIGS. 26(c) and 26(d) show a higher-magnification view of the SASC layer, where the graphite particles appear as black particles surrounding the blue Ni-rich regions FIG. 26(d). FIGS. 26(e) and 26(f) show the Ni-enriched regions from the SASC layer, which appear as bright islands. FIGS. 26(e) and 26(f) highlight the Ni-enriched regions within the SASC layer. FIG. 26(f) shows these Ni rich regions or islands which sometimes contain dispersed Bi-enriched phases, since the C89839 alloy has bismuth.

[0280] The samples show successful formation of SASC layers of thicknesses ranging from 110 μm (≈0.00433 in) to 785 μm (≈0.0309 in). The microstructure shows enrichment in Ni and incorporation of graphite particles in the surface regions of the casting. The Ni coating present on the Ni-coated graphite particles and the Ni powder in the slurry coated on the cores led to an increase in the Ni wt % near the surface of the casting. In the surface alloyed and surface composited surface layer, the graphite particles are present around the Ni-rich islands, instead of being incorporated within the Ni-rich islands.

[0281] The presence of Ni coating on graphite particles presumably increased the wettability between the molten metal and the graphite particles and improved the adhesion between the graphite particles and the SASC layer. The SASC samples exhibited a high density of Ni-rich islands (approximately 41% area fraction), and they appear as numerous bright regions distributed throughout the layer (marked by white arrows in FIGS. 26(a) and 26(b)). When uncoated graphite powders were mixed in the slurry, there was no incorporation of graphite particles in the surface alloyed layer, demonstrating the critical role of Ni coating on the graphite particles for the incorporation of graphite particles in the surface layer of castings.

[0282] FIG. 27(a) shows the average thickness of the surface layers formed on C89836 brass substrate using Ni—Cu powders and Ni—Cu+Ni-Graphite powders in the slurry during the casting process. The surface alloyed and surface composited samples formed thinner layers when Ni—Cu+Ni-Graphite powders were incorporated in the slurry, measuring 315±35 μm (0.0124±0.0014 inches) with PVA and only 110±15 μm (0.0043±0.0006 inches) when PVA+Superplasticizer was used to form slurry (compared to the thickness of the surface alloyed layer from a prior study where only Ni and Cu powders were used in the metal slurry with PVA as the binding medium). The choice of binder in the slurry influences the thickness and percent coverage of the surface layer.

[0283] When Ni-coated graphite particles, with 58 wt % Ni and 42 wt % Graphite, were added to the slurry mixture, the area percentage of graphite particles in SASC layer was quantified. As seen in FIG. 3 (b), the SASC layer, formed when Ni—Cu+Ni-coated graphite particles were used with PVA binder to form the slurry, had the highest surface area coverage at 83±3%; process improvement will lead to 100% coverage of castings by surface alloy and SASC layer.

[0284] As shown in FIG. 28, when the slurry contains PVA+Superplasticizer as binder and Ni, Cu, and Ni-coated graphite powders in the slurry, about 26% area was occupied by graphite particles; under the same conditions, when PVA alone was used as a binder, only 17% area fraction was occupied by graphite particles. When Ni, Cu, and Ni coated graphite powders were present with both PVA and superplasticizer, a high fraction (approximately 41-42% area fraction) of the surface was occupied by Ni-rich islands (FIG. 29). It was observed in prior trials that when uncoated graphite particles were used in the slurry instead of Ni-coated graphite, no graphite was incorporated in the surface layer. Apparently, the Ni coating on graphite enhances the wetting with the melt and facilitates the incorporation of the powders in the slurry by the molten alloy.Compositional and Phase Analysis of SASC Layers

[0285] The elemental analysis of the SASC samples was performed to understand the composition of the phases formed during surface alloying and surface compositing. The increase in the wt % of Ni, alongside the incorporation of graphite particles, specifically in the surface layer, would result in a different microstructure compared to the base alloy or other Ni-rich alloys, such as Monel-400. The slurry composition consisted of pure Ni and Cu powders and Ni-coated graphite powders. The total quantity of Ni added to the system will be the sum of the Ni from the pure Ni powder and the Ni coating on the graphite particles. The purpose of this addition was to increase the Ni concentration of the surface layer, which would improve the corrosion resistance of the SASC layer. As discussed in the prior section, islands of Ni-rich phase were observed across the surface modified layer with the graphite particles present between these islands. The composition of typical Ni-rich islands is shown in FIG. 30(b), where spectrum 1 in the Ni-rich island has a Ni concentration of 46.58 wt %, which is significantly higher than the C89836 base alloy (~0.9 wt % Ni) as shown in FIG. 30. The average Ni concentration in the SASC layer was around 21.06 wt %, indicating successful enrichment of Ni in the SASC layer (compared to 0.9 wt % Nickel present in the base alloy).

[0286] FIG. 31 shows the elemental mapping of the SASC layer showing the distribution of Ni, Cu, C, and Zn. The composition of the SASC layer differs significantly from that of the base alloy. While the base is mainly Cu and Zn, the SASC layer shows a much higher concentration of Ni, and it also incorporates graphite particles. EDS map scans confirm the presence of the graphite particles, which are rich in carbon, and show Ni and Cu rich layers forming around the graphite particles.

[0287] The EDS composition scan in FIG. 32 and the EDS Elemental Dot Mapping in FIG. 33 of the SASC layers. FIG. 33 showed the presence of both Ni and Cu enriched regions which were surrounded by graphite particles. The EDS Line Scan in FIG. 34 shows an increase in the Ni and Cu concentrations around the periphery of the graphite particles. The Ni-rich zone surrounding the graphite particle was approximately 10 μm wide with the Cu concentration increasing to normal levels at a distance of 15 μm from the surface of the graphite particles.X-Ray Diffraction Pattern of the Base Alloy, SA Layer, and SASC Layer

[0288] In the case of yellow brass (60 / 40 Cu—Zn), the microstructure is composed of two phases, α and β phases. The α phase is rich in Cu, while the β phase is rich in Zn. The X-Ray Diffraction pattern of the base alloy shows the formation of a Cu—Ni—Zn phase as well as a Cu—Sn phase, which are expected on account of the composition of the base alloy which contains 4-7 wt % Sn and 2-4 wt % Zn. Bismuth, which was added to the melt for machinability, forms Bi particles during solidification, which are identified as the peak at 30°, shown in FIG. 35.

[0289] The X-Ray Diffraction pattern of the surface alloyed layer (formed when the Ni and Cu were included in the slurry) shows the formation of Ni-rich phases, which were not observed in the base C89836 alloy. As the slurry contained pure Ni and pure Cu powders, and the base alloy had 90% Copper and 0.9% Nickel, the surface alloyed layer contained a Ni—Cu solid solution phase. The X-Ray Diffraction pattern of the SASC layer showed the presence of Cu—Ni solid solution, Cu—Zn solid solution, and graphite particles.

[0290] The graphite particles were identified at a 2θ of 26.5°, confirming their presence. The Ni—Cu solid solution phase was visible as a smaller peak next to the Cu—Zn peak, but the same was not visible for the yellow brass or C89836 samples. C89836 has approximately 0.9 wt % of Ni, this amount is not enough for the formation of a significant amount of Ni—Cu phase. This changes on the addition of Ni powder as well as the Ni added through the Ni-coated graphite particles in the SASC layer. The localized increase of Ni concentration in the SASC layer leads to the formation of the Ni—Cu phase.Corrosion and Leaching Studies

[0291] A bar chart (FIG. 36) compares the average corrosion current (Icorr) for different surface-alloyed (SA) layer types, showing their relative resistance to corrosion. Since a higher Icorr corresponds to a higher corrosion rate (i.e., lower corrosion resistance), the comparison directly reflects material performance. Cu60Zn40 brass showed the highest Icorr (~1.3 μA), confirming its poor corrosion resistance. The base alloy, C89836, performed better (~0.70 μA), while Ni—Cu surface-alloyed castings further reduced Icorr to ~0.11 μA. The SASC layer, formed by incorporating Ni, Cu, and Ni-coated graphite, achieved the lowest values (0.05-0.13 μA). Among binder systems, PVA+Superplasticizer yielded the best performance (~0.05 μA). Small error bars confirmed the consistency of results. Overall, the castings with the SASC layer had the lowest corrosion rate, indicating that the SASC technique improves the corrosion resistance.

[0292] The galvanic potential difference between Monel and graphite is expected to be lower in tap water than in seawater. This reflects the environment-specific nature of the galvanic series: seawater, with its high conductivity and chloride content, amplifies potential separations and galvanic currents, while potable tap water has one to two orders of magnitude lower conductivity and far fewer aggressive ions, compressing potential differences and reducing galvanic driving forces. In chloraminated tap water (~2 ppm chloramine), the environment remains mildly oxidizing but less aggressive than aerated seawater. Under these conditions, Ni—Cu alloys with near-Monel compositions form stable passive films that shift their potentials to more noble values, while graphite remains near the oxygen reduction potential. The result is a reduced ΔE between near Monel composition and graphite in chloraminated potable water compared with seawater. The observed improvement in corrosion resistance of the graphite-Monel-brass composite is consistent with the reduction in galvanic potential differences in tap water relative to seawater, as well as the protective role of the Monel-like coating.

[0293] Lead leaching is another concern in brass alloys. Even when not deliberately added for machinability, residual lead can remain from recycled feedstock and subsequently leach into drinking water, where it poses serious health risks including birth defects and cancer. EPA regulations limit lead in drinking water to 15 ppb and restrict its addition in alloys to 0.25 wt %. Leaching tests were conducted over a 24-hour period at room temperature using an NSF-61 derived procedure. Controls with DI water and tap water established baseline concentrations and confirmed test reliability, as shown in FIG. 37.

[0294] Two as-cast samples, SASC and C89836, were tested in this study using a method that was derived from the NSF-61 test. The surface of the sample was exposed to a column of tap water, 30 ml in volume (≈1.8 in3), with a contact area of 1.77 cm2 (≈0.27 in2) at room temperature. Following the 24-hour period, the test liquid was analyzed using ICP-MS to quantify the lead concentration in parts per billion (ppb). It was observed that the water in contact with SASC layer, containing Ni, Cu, and Ni-graphite powders, did not have any lead leached into the water, whereas the base alloy, C89836, leached lead into the water, up to 1.43 ppb. The control sample of tap water had a lead concentration of 0.08 ppb, while in DI water, lead was not detected, showing the reliability of our testing technique. These preliminary tests indicate that surface alloyed and surface composited castings show reduced leaching of lead in water. It appears that the lead present in the base alloy does not contact the water due to the surface alloyed or SASC layer formed on the surface of the castings. The Ni-rich phase incorporating graphite particles reduces corrosion as well as leaching, in addition graphite is inert and will reduce any leaching in water.Machinability of Surface Alloyed and Surface Composited Layer

[0295] FIG. 38 compares chips collected during machining tests of four brass-based samples. A drill bit was swept across each surface at a cutting depth of 0.010 in (≈0.25 mm). Optical and SEM images are shown for 60-40 brass FIG. 38(a, a1), C89836 alloy FIG. 38(b, b1), Ni—Cu surface-alloyed layer FIG. 38(c, c1), and Ni-graphite SASC layer FIG. 38(d, d1). Higher-magnification SEM images FIG. 38(e, e1) include carbon mapping of the SASC chips, where green dashed circles highlight carbon-enriched regions. These confirm that embedded graphite particles promote chip breaking and thereby improve machinability. All images include a stereoscope millimeter scale bar (red, 1 mm (≈0.0394 in)) for reference.

[0296] Machining of 60-40 brass FIG. 38(a, a1) produced long, continuous ribbons, reflecting high ductility and poor chip breakage, making it difficult to machine. C89836 alloy FIG.38(b, b1) formed shorter, curled chips that were more fragmented, an effect attributed to bismuth additions that aid chip breakage. In contrast, the SASC layer FIG. 38(d, d1) produced the smallest and most granular chips, consisting of short segments and fine particles. This morphology indicates improved machinability due to the presence of graphite, which acts as a chip-breaking phase. Overall, chip size decreased progressively from 60-40 brass to C89836, to Ni—Cu SA, and finally to SASC, demonstrating a clear trend toward more fragmented, granular chips.

[0297] The results show that machinability improvements traditionally achieved by adding Pb or Bi can instead be realized through incorporation of Ni and graphite in a SASC layer. This provides a path to replace toxic alloying elements with a safer, surface-engineered alternative.

Examples

example embodiments

[0109]Embodiment 1: A low-cost method of producing a cast copper-based alloy component having an enriched, corrosion-resistant and wear-resistant surface, the method comprising:[0110](a) providing a copper-based alloy selected from the group consisting of yellow brass and red brass;[0111](b) preparing a slurry comprising:[0112]at least one powder selected from the group consisting of Cu, Ni, Cu—Ni, Cu—Sn, Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and Ni-coated SiC; and[0113]a binder medium selected from the group consisting of water-based or alcohol-based binders, or superplasticizer;[0114](c) coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold; optionally repeating coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold;[0115](d) heating the copper-based alloy to a temperature in the range of 1200° C. to 1300° C. or higher;[0116](e) pouring the molten c...

example 1

Surface Alloying and Surface Compositing of a Brass Alloy Castings Using Mold and Core Coatings

[0150]This work presents a low-cost casting process for surface alloyed surface compositing (SASC) of C89836 brass castings. Surfaces of the sand cores were coated with slurries containing varying amounts of Cu, Ni, and reinforcement particles, including Ni-coated Al2O3 and Ni-coated SiC powders, before pouring brass melts into the molds. In SASC samples, Al2O3 and SiC particles were concurrently incorporated into the casting surface, forming a surface composited region. Microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed the formation of a Ni-enriched surface and the successful incorporation of SiC or Al2O3 particles on the casting surface. Electrochemical testing indicated that SASC castings containing Al2O3 and SiC particles exhibited reduced corrosion rates compared to the base alloy. The SA and SASC ...

example 2

Factors Considered for Creating Alloyed and Composited Surface Layers on Brass

Introduction

Brass components in water distribution systems are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from metal leaching.

The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure. The proposed surface alloying process significantly enhances the durability of brass components by targeting corrosion reduction at its surface. This process is practical and cost-effective, easily integrated into existing foundries without additional...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority to U.S. Provisional Patent Application No. 63 / 781,159, filed Mar. 31, 2025, the contents of which are incorporated by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Federal Grant No. 2113857 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD OF THE INVENTION

[0003] The disclosed technology is generally directed to forming surface alloyed and surface composited layers on surfaces during casting. More particularly, the technology is directed forming surface alloyed and surface composited surfaces on copper alloy castings.BACKGROUND OF THE INVENTION

[0004] Brass components are common in water distribution systems; however, brass components are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from harmful metal leaching from the casting into water. The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure.

[0005] Surface alloying is a surface engineering technique that modifies the surface composition of materials to improve specific properties like wear resistance, hardness, and corrosion resistance. While techniques like laser surface alloying, chromizing, and bronzing have been explored, they are expensive and difficult to scale up and are difficult to apply to internal surfaces of components since they require a line of sight and are not universally applicable to copper alloys. Accordingly, a need exists for lower cost, corrosion resistant, leaching resistant, wear resistant, and machinable brass articles and methods of making the same.SUMMARY

[0006] Disclosed herein are lower cost, corrosion resistant, leaching resistant, wear resistant, and machinable brass articles and methods of making the same.

[0007] Disclosed herein is a method of making a copper alloy article, including providing a slurry, applying the slurry to an insulating tooling to form a slurry-coated tooling, contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy, and solidifying the molten copper alloy and surface modified layer. The slurry includes a surface modifying material and a liquid binder. The surface modifying material includes a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof.

[0008] In some cases, the surface modifying material includes Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof, the metal-coated ceramic includes Ni-coated SiC, Ni-coated Al2O3, or any combinations thereof. In some cases, the metal-coated carbon-containing compound includes Ni-coated graphite. The surface modifying material includes particles. In some cases, the surface modifying material comprises particles comprising at least one dimension ranging from about 5 μm to about 300 μm. In certain cases, the surface modifying material includes Cu and Ni and, and the ratio of Cu and Ni is about 1:1.

[0009] In another aspect, the liquid binder comprises water, a polymer, or any combinations thereof. The polymer can include polyvinyl alcohol. In certain embodiments, the liquid binder includes about 0.5 wt % to about 30.0 wt % polymer, based on the total weight of the liquid binder. In some cases, the liquid binder can include a superplasticizer.

[0010] In another aspect, the insulating tooling is a sand mold, a sand core, or any combination thereof. In some cases, the molten copper alloy has a temperature above about 1200° C.

[0011] Another aspect of the methods disclosed herein includes applying the slurry to an insulating tooling and further includes drying the slurry. In some cases, the steps of providing a slurry and applying the slurry to an insulating tooling to form a slurry-coated tooling are repeated two or more times to form a multi-layered slurry-coated tooling.

[0012] Also disclosed herein are corrosion-resistant articles. The articles include a cast copper alloy component and a surface modified layer disposed on a surface of the cast copper alloy component, the surface modified layer comprising a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. In some cases, the cast copper alloy component is includes yellow brass, red brass, bronze, or any combinations thereof.

[0013] In some cases, the surface modified layer Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In certain examples, the surface modified layer is about 1 μm to about 5 mm thick.

[0014] In another aspect of the articles disclosed herein, the corrosion rate of the corrosion resistant article is reduced by 45% to 90%, as compared to the corrosion rate of the cast copper alloy component.

[0015] In another aspect of the articles disclosed herein, the corrosion-resistance article comprises a reduced leach rate of one or more elements into water, as compared to the leach rate of one or more elements into water of the cast copper alloy component.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.

[0017] FIG. 1 shows a schematic of an exemplary embodiment of the methods disclosed herein. Dotted lines indicate optional steps.

[0018] FIG. 2 shows a schematic illustration of the manufacturing process for surface alloyed / surface composited (SASCs).

[0019] FIG. 3 shows scanning electron micrographs of powders used to make the slurry. Panel (a) shows pure Cu powder, panel (b) shows pure Ni powder, panel (c) shows Ni-coated SiC, pane (d) shows Ni-coated Al2O3, panel (e)-(e3) shows elemental image of mounted Ni-Coated SiC particle, and panel (f)-(f3) shows elemental image of mounted Ni-Coated Al2O3 particle.

[0020] FIG. 4 shows optical micrographs of the SASC layer incorporating SiC particles at, in panel (a), low magnifications and, in panel (b), shows high magnifications. The dark regions in panel (a) correspond to Ni-enriched islands formed in situ during solidification. Panel (c) shows area elemental analysis comparing the SASC layer and the base alloy. Panel (d) shows elemental analysis of the phases present within the SASC layer. Panels (e)-(e4) show elemental maps of the SASC layer.

[0021] FIG. 5 shows optical micrographs of the Al2O3-reinforced SASC layer at, in panel (a) low magnifications and, in panel (b), high magnifications. The light regions correspond to Ni-enriched islands formed in situ during solidification. Panel (b) shows highlights the interfacial integrity between the reinforcement particles and the SASC layer. Panel (c) shows area elemental mapping for the SASC sample reinforced with Ni-coated Al2O3 particles, showing a higher Ni content in the SASC layer than in the base alloy. Panel (d) shows elemental analysis of the individual phases present within the SASC layer. (e)-(e4) Elemental maps comparing the SASC layer with the base alloy.

[0022] FIG. 6 shows, in panel (a) and in panel (c), area fraction and average particle size of Ni-rich islands and embedded reinforcements within the SASC layers containing SiC and Al2O3 particles, respectively. Panels (b) and (d) show area fraction and average particle size of Bi precipitates in the corresponding SASC layers, respectively.

[0023] FIG. 7 shows, in panel (a) and in panel (b), SASC layer thickness and surface coverage measured in the cast SASCs, respectively. Panel (c) and panel (d) show Ni-depleted zone length and Ni shell thickness in the cast SASCs, respectively.

[0024] FIG. 8 shows corrosion current results from the Potentiodynamic cell test.

[0025] FIG. 9 shows microhardness results of the S0 base alloy and SASC sample.

[0026] FIG. 10 shows an X-ray diffraction (XRD) plot of the Al2O3 and SiC SASCs.

[0027] FIG. 11 shows adhesion test results of the SASC samples with Ni—Al2O3 (S1) and Ni—SiC (S3) before heating (in panel a1 and panel b1), after heating to 250° C. (panel a2 and panel b2), and after heating to 400° C. (panel a3 and panel b3) and rapidly cooling by water quenching to room temperature. There is no delamination of the SASC layer.

[0028] FIG. 12 shows machinability test showing the formation of chips from the surface machining of, in panel (a), yellow brass, in panel (b), base alloy C89836, in panel (c), base alloy with surface alloyed layer and, in panel (d) base alloy with SASC layer containing Al2O3 particles. The image in panel (d) shows much smaller chips.

[0029] FIG. 13 shows, in panel (a) an electron micrograph and associated elemental analysis of the individual phases present within the SASC layer (Spectrum 1) and the base copper alloy (Spectrum 2). Panel (b) shows corrosion rate of the surface alloyed casting as compared to un-modified red brass and yellow brass. Panel (c) shows a picture of a cross section of a sample, with the surface alloyed layer circled.

[0030] FIG. 14 panel (a) shows optical microstructure of cross-section of casting showing the surface alloyed (SA) layer and base metal shows some porosity) in panel (b) shows SEM / EDS data showing the elemental gradients of Ni, Cu, Zn, and Sn from the SA layer toward the substrate Bi-Alloy, including enrichment of Nickel in the surface alloyed layer. Panel (c), and panel (d) show SEM / EDS data showing the elemental gradient of Zn and Cu within the SA layer and substrate yellow brass, including higher copper content in the SA layer compared to the base alloy.

[0031] FIG. 15 panel (a) shows yellow brass castings made at RheoCast Foundry using the surface alloying process on coated molds, panel (b) shows molds and cores used to cast internally surface alloyed Bi-Alloy castings, panel (c) shows water industry casting made using bi-alloy and coated cores.

[0032] FIG. 16 shows the highest thickness of surface alloyed layer alongside the sample numbers corresponding to samples described in Table 8.

[0033] FIG. 17 shows optical microscope images of samples described in Table 8. All scale bars are 500 μm.

[0034] FIG. 19 shows an electron micrograph and corresponding EDS map of Si and Ni elements from a portion of the surface alloyed layer of sample 47.

[0035] FIG. 18 shows Ni—Cu phase diagram.

[0036] FIG. 20 panel (a) shows final casting of sample S9 of Table 16 showing the surface alloyed layer, panel (b) shows metallographically prepared sample etched with Copper No 2 etchant showing the Ni enriched layer, panel (c) shows microstructural image of the sample S9 showing the surface alloyed layer and base metal.

[0037] FIG. 21 shows an optical micrograph of sample S9 of Table 16, showing SA layer with an average thickness of 1.2 mm.

[0038] FIG. 22 shows an electron micrograph of Sample S9, showing elemental analysis maps by EDS for Cu, Ni, Sn, C, and Zn. Elemental composition is also given as a function of distance for a line trace crossing from the SA layer to the bulk metal is indicated on the electron micrograph.

[0039] FIG. 23 shows an electron micrograph of Sample S18, showing elemental analysis by EDS for Cu, Ni, Sn, C, and Zn. Elemental composition is given as a function of distance for a line trace crossing from the SA layer to the bulk metal is indicated on the electron micrograph.

[0040] FIG. 24 shows an electron micrograph of Sample S27 of Table 16, with inset indicating locations where elemental analysis was performed for Al, Cu, and Zn and shown in Table 23.

[0041] FIG. 25 shows in panels (a) and (c), cores from industry partner coated with metal powder slurry, and in panel (b) an as-cast surface alloyed component.

[0042] FIG. 26 shows polarized optical micrographs showing the microstructure of the surface-alloyed and surface composited layer (using PVA binder) formed on C89836 brass casting. The images show distinct surface-alloyed and surface composited layers composed of blue Ni-rich regions (islands), dark graphite particles and multiphase microstructure. Panel (a) and panel (b) show low magnification image from the SASC layer. Panel (c) and panel (d) show regions between Ni-rich islands containing graphite particles. Panel (e) and panel (f) high magnification view of the Ni-rich regions (islands) occasionally containing Bi-rich phase within them, and graphite particles around the Ni-rich regions.

[0043] FIG. 27 shows, in panel (a), the average thickness of three types formed of surface layers on C89836 brass substrate during the casting process. Panel (b) shows the average surface coverage observed in the three types of surface layers on C89836 brass castings using different slurry compositions.

[0044] FIG. 28 shows the area percentage of graphite particles within the SASC layer formed on C89836 brass castings with PVA and with PVA+Superplasticizer used as the binders.

[0045] FIG. 29 shows the distribution and morphology of nickel-rich islands within the three surface alloy layer types formed on C89836 brass castings. Panel (a) shows the area percentage, while panel (b) shows the average size of the Ni-rich islands.

[0046] FIG. 30 shows SASC sample with incorporation of Ni-coated Graphite powder in the slurry showing formation of Ni-rich islands and incorporated graphite particles in the SASC layer. (Sample 2)

[0047] FIG. 31 shows elemental mapping showing the presence of Ni, Cu, Zn and graphite in the SASC layer. Enrichment in Ni is observed around the graphite particles.

[0048] FIG. 32 shows SASC sample with Ni-Graphite showing formation of Ni-rich islands in the SASC layer (Sample 1), which are surrounded by graphite particles.

[0049] FIG. 33 shows elemental mapping showing the presence of Ni, Cu, and Zn in the SASC layer. Ni distribution is visible around the graphite particles.

[0050] FIG. 34 show line scans showing an increase in Ni (bottom right) and Cu (bottom left) along the surface of graphite particles, incorporated in the SASC layer.

[0051] FIG. 35 shows XRD mapping of the SASC sample showing the presence of graphite and Cu—Ni phase.

[0052] FIG. 36 shows a comparison of Icorr for yellow brass, C89836, and the SA and SASC samples showing an increase in corrosion resistance on account of surface modification.

[0053] FIG. 37 shows a comparison of lead concentration in water in ppb, for base alloy, SASC sample, and the water control samples.

[0054] FIG. 38 shows comparison of chips collected during machining of three different brass-based samples, produced by sweeping a drill bit across the surface of each material at a cutting depth of 10 in / 1000. Optical and SEM images of chips formed during machining tests of the 60-40 alloy (panels a and a1), the C89836 alloy (panels b and b1), the Ni—Cu SA layer (panels c and c1), and the Ni-Graphite SASC layer (panels d and d1). Panels (e and e1) present higher-magnification SEM images of the chips in (d1), with corresponding carbon mapping, showing graphite particles embedded in the SASC layer. The dashed circles indicate carbon-enriched regions, indicating how the embedded graphite particles promote breaking of chips and thereby enhances the machinability of the SASC samples.DETAILED DESCRIPTION OF THE INVENTION

[0055] Disclosed herein are corrosion resistant, wear resistant, and / or leaching resistant articles and methods of making the same. More specifically, disclosed herein are corrosion resistant copper alloy (e.g., brass such as yellow brass or red brass, bronze alloys, and other copper alloys) articles and methods of making the same. As used herein, the terms “copper alloy” and “brass” and “bronze” are used synonymously. The present disclosure describes a low-cost surface alloying and / or surface compositing method that enriches the surface of a brass casting with selected materials that increase corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance, and / or that incorporate particles including graphite, silicon carbide, and / or alumina on the surface of castings to impart wear resistance and machinability.

[0056] In some examples, the methods disclosed herein include a step of applying a slurry to tooling to form a slurry-coated tooling. As used herein, “casting tooling” or “foundry tooling” or “tooling” refers to the engineered components used to create the geometry of a casting, including molds and cores. As used herein, the term “tooling” refers to molds, cores, and combinations thereof. In some cases, tooling may be made from sand, metal, ceramic, graphite, or other refractory materials.Methods

[0057] Referring to FIG. 1, disclosed herein is a method of making a copper alloy article (1). The method includes providing a slurry (100) including a surface modifying material and a liquid binder. The surface modifying material can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. The method further includes applying the slurry to an insulating tooling to form a slurry-coated tooling (200). The method further includes contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy, (300) and solidifying the molten copper alloy and surface modified layer.

[0058] In some examples, the method disclosed herein includes providing a slurry including a surface modifying material and a liquid binder. As used herein, a “slurry” refers to a mixture of solid particles dispersed in a liquid. The slurry includes at least one surface modifying material. As used herein, the term “surface modifying material” refers to a material present on the surface of tooling and interacting with hot, molten copper alloy, creating a modified layer on at least one surface of a copper alloy casted component. The resulting surface modified layer is formed between the bulk of the copper alloy and the tooling, and resides on the surface of the cast component produced as result of the methods disclosed herein.

[0059] In some cases, the surface modified layer is a surface alloyed layer, a surface composited layer, or a combination thereof. As used herein, “surface modified layer” refers to a surface-confined modification of a component having a bulk metallic component, such as copper alloy like brass or bronze. As used herein, “surface alloying” refers to the process where the molten copper alloy interacts with a metallic surface modifying material on a surface of tooling to produce a surface region which is enriched in metallic alloying elements (e.g., Cu, Ni, Bi, Sn, etc.). This enriched region may, for example, enhance corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance. In some cases, interacting refers to melting. In some cases, interacting at the surface refers to dissolution. As used herein, “surface compositing” refers to the process where non-metallic surface modifying components (e.g, uncoated graphite, uncoated SiC, uncoated Al2O3, metal-coated graphite, metal-coated Al2O3, metal-coated SiC, other solid lubricants and ceramic particles, and any combinations thereof) are incorporated in the surface region of the castings of copper alloys. In some cases, non-metallic surface modifying components are transferred from the slurry to the molten copper alloy to form a surface composite on the resulting copper alloy article. In some cases, non-metallic surface modifying components are transferred from the slurry-coated tooling to the surface of the cast copper alloys to form a surface composite on a surface of a resulting copper alloy article

[0060] Surface modifying materials can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. In some cases, the surface modifying material may include one or more metals. More specifically, the surface modifying material may include Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In some cases, the metal-coated alloying materials may be coated with nickel or copper (e.g., Ni-coated graphite, Ni-coated Al2O3, Ni-coated SiC, Cu-coated graphite, Cu-coated Al2O3, Cu-coated SiC).

[0061] In some cases, the surface modifying material includes an alloying element. In some cases, the alloying element includes a metal. Examples of metal may include Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Al, Ga, In, Sn, Tl, Pb, Bi, Po, or any combinations thereof.

[0062] In some cases, the surface modifying materials include a metallic alloy. Examples of metallic alloy may include Cu—Sn, Cu—Zn, Cu—Ni, Cu—Al, Cu—Be, Cu—Si, Cu—Mn, Cu—P, Ni—Cr, Ni—Fe, Ni—Mo, Ni—Cu, Ni—Co, Ni—Ti, Fe—C, Fe—Cr, Fe—Cr—Ni, Fe—Mn, Fe—Si, Fe—Ni, Fe—Mo, Fe—W, Al—Si, Al—Mg, Al—Cu, Al—Zn, Al—Mn, Al—Li, Mg—Al, Mg—Zn, Mg—Mn, Mg—Y, Mg—Gd, Ti—Al, Ti—V—Al, Ti—Nb, Ti—Mo, Co—Cr, Co—Cr—Mo, Zn—Al, Zn—Cu, Zn—Mg, or any combinations thereof.

[0063] In some cases, the surface modifying materials include a carbon-containing compound. Examples of carbon-containing compounds include diamond, graphite, amorphous carbon, lonsdaleite (hexagonal diamond), fullerenes (c60, c70, etc.), carbon nanotubes (single-walled, multi-walled), graphene, graphene oxide, reduced graphene oxide, activated carbon, glassy carbon, carbon black, soot, charcoal, coke (petroleum coke, metallurgical coke), nanofoam carbon, carbon aerogel, q-carbon, carbyne, amorphous diamond (tetrahedral amorphous carbon), turbostratic carbon, or any combinations thereof. In some cases, the carbon-containing compound may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0064] In some cases, the surface modifying materials include a ceramic. In some cases, the ceramic includes oxides (e.g., Al2O3, ZrO2, SiO2, MgO, CaO, HfO2, ThO2, BeO, ZnO, TiO2, Cr2O3, spinels, perovskites, mullite, cordierite, zircon, magnesium silicates), carbides (e.g.SiC, WC, B4C, TiC, TaC, NbC, VC, HfC, Cr3C2), nitrides (e.g., Si3N4, AlN, BN, TiN, ZrN, HfN, CrN), oxynitrides (e.g., SiAlON, AlON), borides (e.g., TiB2, ZrB2, HfB2, CrB2), silicides (e.g., MoSi2, WSi2, TiSi2, CrSi2), refractory silicates & phyllosilicates (e.g., Al2Si2O5(OH)4, Mg3Si4O10(OH)2, Al2Si4O10(OH)2, montmorillonite / bentonite clays), and any combinations thereof. The incorporation of ceramic particles may improve the wear resistance of castings and reduce the leaching of harmful elements in water. In some cases, the ceramic particles may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0065] In some cases, the surface modifying material includes a solid lubricating material. Examples of solid lubricating materials include graphite, molybdenum disulfide, tungsten disulfide, hexagonal boron nitride (h-BN), Pb, Sn, Ni, In, bismuth oxide, copper oxide, silicon nitride, silver-based lubricating phases, barium fluoride, calcium fluoride, or any combinations thereof.

[0066] In some cases, the surface modifying material is a powder. In some cases, the powder includes particles. In some cases, the particles have at least one dimension ranging from about 1 μm to about 1000 μm, from about 3 μm to about 500 μm, from about 5 μm to about 300 μm, or from about 10 μm to about 250 μm. In some cases, the Ni particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 50 μm to about 175 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Al particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Cu particles have at least one dimension ranging from about from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the Bi particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 10 μm to about 170 μm, from about 8 μm to about 200 μm, from about 10 μm to about 200 μm, or from about 5 μm to about 215 μm. In some cases, the Cu—Sn particles have a particles size ranging from about 5 μm to about 500 μm, from about 50 μm to about 100 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. In some cases, the metal-coated Al2O3 particles have at least one dimension ranging from about 5 μm to about 500 μm, from about 25 μm to about 275 μm, from about 10 μm to about 300 μm, from about 15 μm to about 275 μm, or from about 50 μm to about 250 μm. In some cases, the metal-coated graphite particles have at least one dimension ranging from about 16 μm to about 200 μm, from about 5 μm to about 500 μm, from about 25 μm to about 275 μm, from about 10 μm to about 300 μm, from about 15 μm to about 275 μm, or from about 50 μm to about 250 μm. In some cases, the metal-coated SiC particles have at least one dimension ranging from about 10 μm to about 100 μm, from about 5 μm to about 500 μm, from about 50 μm to about 175 μm, from about 10 μm to about 200 μm, or from about 15 μm to about 215 μm. There are several suitable methods and standards for determining particle size, including ASTM E11, ASTM B822, ASTM E112, and ASTM E2651. For example, according to ASTM B822, particle size distribution can be determined using laser diffraction based on Fraunhofer diffraction, Mie scattering, or a combination of both. The scattering data are analyzed by assuming a spherical particle model; therefore, the reported particle size is expressed as an equivalent spherical diameter. In other words, the particle size corresponds to the diameter of a sphere having the same scattering characteristics (or projected area) as the actual particle.

[0067] In some cases, the surface modifying material includes a combination of Ni particles, Cu particles, and at least one non-metallic particle. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0068] In some cases, the surface modifying material includes Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al. In some cases, the ratio of Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al is about 1:1. In some cases, the ratio of Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al is about 100:1, about 50:1, about 25:1, about 10:1, about 9:1, about 5:1, about 4:1, about 3:1, about 2:1, about 1:1, about 1:2, about 1:3, about 1:4, about 1:5, about 1:9, about 1:10, about 1:25, about 1:50, or about 1:100.

[0069] In some cases, the surface modifying material includes at least one pair selected from Cu and Ni, Cu and Al, or Cu and Sn, or Ni and Al. For example, if Ni and Cu metals are selected, the surface modifying material may include a powder mixture of Ni particles and Cu particles. In another example, in the case where Cu and Sn are selected, the surface modifying material may include an alloy powder of Cu—Sn particles. For example, the alloy powder of Cu—Sn may be a a 90-10 alloy of Cu—Sn. The surface modifying material further includes at least one non-metallic particle. In some cases, the surface modifying material includes Cu and Ni and at least one non-metallic particle. In some cases, the ratio of Cu to Ni to the at least one metal-coated non-metallic particle is about 1:1:0.1, about 1:1:0.2, about 1:1:0.3, about 1:1:0.4, about 1:1:0.5, about 1:1:0.6, about 1:1:0.7, about 1:1:0.8, about 1:1:0.9, about 1:1:1.

[0070] In some cases, the slurry includes about 1:1:0.6 ratio of Cu, Ni, and metal-coated non-metallic particle and about 10 wt % polymer in a solvent, based on the total weight of the polymer and solvent. In some cases, the metal-coated non-metallic particle includes Ni-coated Al2O3, Ni-coated SiC powders, or a combination thereof. In some cases, the slurry further includes a superplasticizer.

[0071] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Ni, based on the total weight of the surface modifying materials in the slurry.

[0072] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Cu, based on the total weight of the surface modifying materials in the slurry.

[0073] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 20 wt % to about 30 wt %, about 22 wt % to about 28 wt %, or about 23 wt % to about 26 wt % of a non-metallic particle, based on the total weight of the surface modifying materials in the slurry. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0074] In some instances, the slurry may include about 0.1 wt % to about 50 wt %, about 1.0 wt % to about 30 wt %, about 0.1 wt % to about 8.0 wt %, about 0.2 wt % to about 10 wt %, about 0.3 wt % to about 10 wt %, about 0.5 wt % to about 5.0 wt %, or about 1.0 wt % to about 4.0 wt % of bismuth, based on the total weight of the surface modifying materials in the slurry.

[0075] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Sn, based on the total weight of the surface modifying materials in the slurry.

[0076] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Al, based on the total weight of the surface modifying materials in the slurry.

[0077] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Ni—Cu, based on the total weight of the surface modifying materials in the slurry.

[0078] In some instances, the slurry may include about 0.1 wt % to about 80 wt %, about 1.0 wt % to about 50 wt %, about 10 wt % to about 45 wt %, about 15 wt % to about 45 wt %, about 25 wt % to about 40 wt %, about 30 wt % to about 40 wt %, or about 35 wt % to about 40 wt % of Cu—Sn, based on the total weight of the surface modifying materials in the slurry.

[0079] Referring to Example 1, the slurry can include about 38 wt % Cu, about 38 wt % Ni, and about 24 wt % of a non-metallic component. In some cases, the non-metallic component includes a ceramic, a carbon-containing compound, or combinations thereof. In some instances, the non-metallic component is Al2O3, SiC, graphite, or combinations thereof. In some instances, the non-metallic component is metal-coated. In some cases, such as in Example 1, the metal-coated non-metallic particles include Ni-coated Al2O3, Ni-coated SiC, or a combination thereof.

[0080] In another aspect of the methods disclosed herein, the slurry includes a liquid binder. The liquid binder may include water, a polymer, or any combination thereof. In some cases, the liquid binder includes about 0.5 wt % to about 50 wt %, about 0.5 wt % to about 40 wt %, about 1.0 wt % to about 30 wt %, about 2.0 wt % to about 25 wt %, about 3.0 wt % to about 20 wt %, about 4.0 wt % to about 10 wt %, about 4.0 wt % to about 15 wt %, polymer, based on the total weight of the liquid binder. In some cases, the polymer includes polyvinyl alcohol (PVA) or sodium polyacrylate. As shown in the below Examples, other binders which disperse the surface modifying material can be used, such as modified commercial mold and core coatings. For example, modified Refcobar 1010 gel (a water-based core and mold coating with refractory material omitted) or modified Vibrantz binder (a water-based core and mold coating with refractory material omitted) may be used. In some cases, the liquid binder further includes a superplasticizer which leads to increased dispersion and fluidity in the slurry. In some cases, the superplasticizer includes a polycarboxylate superplasticizer (e.g., MEGAPOL GUSR-AC).

[0081] In another aspect, there is a ratio of polymer to surface modifying material in the liquid binder. The ratio of polymer to surface modifying material may be selected based on the viscosity of the resulting slurry. For example, a liquid binder having 4 wt % polymer will have low viscosity and thus, will be added in a lower quantity to act as the binder. Similarly, a liquid binder having 10 wt % polymer solution, due to its higher viscosity, may be added in a slightly higher amount. In some cases, the ratio of surface modifying material to polymer in the liquid binder may include about 40 wt % of surface modifying material to about 10 wt % polymer. For example, approximately 5 grams of 10 wt % polymer was added 13.168 grams of surface modifying material. In some cases, up to about 45 wt % of the surface modifying material to about 10 wt % polymer may be used.

[0082] The methods disclosed herein include a step of applying the slurry to tooling to form a slurry-coated tooling. As used herein, “casting tooling” or “foundry tooling” or “tooling” refers to the engineered components used to create the geometry of a casting, including molds and cores. As used herein, the term “tooling” is used to refer to molds, cores, and other components for casting . . . . In some cases, tooling may be made from sand, metal, ceramic, graphite, or other refractory materials. In some cases, the tooling may include low-thermal conductivity materials (i.e., thermally insulating materials). These “insulating tooling” are intended to absorb heat slowly, minimize thermal shock, and / or control local solidification in the surrounding, cooling molten copper alloy and / or surface modified layer. In some cases, the insulating tooling comprises sand, for example sand mold or a sand core. As used herein, the term “mold” refers to a cavity (e.g., a mold) defining negative space that forms at least one external or internal surface of a cast component. For example, a mold is a shaped cavity into which molten metal is poured to solidify into a desired geometry. The mold provides the negative imprint of the final component. As used herein, the term “core” refers to a shaped insert placed inside a mold to create internal surfaces, hollow sections, or complex internal geometries in a casting. In some cases, where the tooling includes a mold and a core, in addition to or alternative to applying the slurry to a mold (e.g., a sand mold), the slurry is applied to a core (e.g., a sand core) used with a mold, and then the slurry-coated core (and / or mold) is contacted with the molten copper alloy to interact with the slurry to form the surface modified layer. Applying the slurry to tooling to form a slurry-coated tooling may include any suitable method for coating a surface with a liquid mixture, such as painting, brushing, dipping, spraying, flowing, troweling, daubing, or dip-spinning.

[0083] Referring still to FIG. 1, the method may further include drying the slurry-coated tooling (201) before contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy (300). Drying times for the slurry may vary depending upon a thickness of the applied slurry. In some cases, the slurry-coated tooling may be dried for at least about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 19 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, about 24 hours, about 25 hours, about 26 hours, about 27 hours, about 28 hours, about 29 hours, about 30 hours, about 31 hours, about 32 hours, about 33 hours, about 34 hours, about 35 hours, about 36 hours, about 37 hours, about 38 hours, about 39 hours, about 40 hours, about 41 hours, about 42 hours, about 43 hours, about 44 hours, about 45 hours, about 46 hours, about 47 hours, about 48 hours, about 49 hours, about 50 hours, about 51 hours, about 52 hours, about 53 hours, about 54 hours, about 55 hours, about 56 hours, about 57 hours, about 58 hours, about 59 hours, about 60 hours, about 61 hours, about 62 hours, about 63 hours, about 64 hours, about 65 hours, about 66 hours, about 67 hours, about 68 hours, about 69 hours, about 70 hours, about 71 hours, about 72 hours, or more. The slurry-coated tooling may be dried by methods such as air drying or low-temperature furnace drying. The slurry-coated tooling may be dried at room temperature, temperatures above room temperature, or temperatures below room temperature.

[0084] In some cases, still referring to FIG. 1, the steps of providing a slurry (100) and applying the slurry to an insulating tooling to form a slurry-coated tooling (200) may be repeated (400) multiple times to form a multi-layered slurry-coated tooling. In some cases, the step of drying the slurry-coated tooling (201) may be repeated (500). In some cases, the slurries used in subsequent repeats of steps (100) and (200) are substantially compositionally the same as earlier-applied slurries. In some cases, the slurries used in subsequent repeats of steps (100) and (200) are substantially compositionally different than earlier-applied slurries.

[0085] The methods disclosed herein further include contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy. Contacting the slurry-coated tooling with molten copper alloy includes any suitable method for introducing a liquid metal to a tooling, such as pouring, ladling, pressure-assisted filling (e.g., gas-pressurized filling, low-pressure casting), gravity sand casting, injection, centrifugal casting, vacuum-assisted pouring (e.g., counter-gravity casting), or squeeze casting. In some cases, the method further includes pouring the molten copper alloy in the slurry-coated tooling to synthesize a surface modified layer on the cooper alloy casting upon the completion of solidification of the molten copper alloy. The method further includes pouring the molten copper into the mold and the slurry-coated core forms a surface modified layer through interfacial interaction during the solidification of the molten copper alloy.

[0086] Contacting the slurry-coated tooling with molten copper alloy includes heating the copper-based alloy (e.g., to a temperature above the melting point of the copper alloy, such as a temperature above 1200° C., or a temperature between about 1200° C. to about 1300° C., or to a temperature higher than 1300° C., described further elsewhere herein) and pouring the molten copper-based alloy into the (coated) tooling. As a result, at least part of the applied slurry may interact with the molten copper-based alloy at the surface to form the surface modified layer on the surface of the casting. The surface modified layer is disposed between the slurry-coated insulating tooling and the bulk copper alloy. In some cases, heating the molten copper alloy to a temperature exceeding its melting temperature (i.e., a superheat) before it is poured into the slurry-coated tooling may be desirable. As used herein, “superheat” refers to the amount by which the temperature of the molten copper alloy exceeds its melting temperature before it is poured into a mold. For example, if a brass alloy has a melting temperature of 930° C. and it is poured into a mold at a temperature of 1030° C., the superheat is 100° C. In some cases, a superheat of about 50° C., about 100° C., about 150° C., about 200° C., about 250° C., about 300° C., about 350° C., about 400° C., about 450° C., or about 500° C. may be used in the methods disclosed herein. In some cases, contacting the slurry-coated tooling with molten copper alloy (300) may include heating the tooling in advance of pouring the molten copper-based alloy into the (coated, heated) tooling. In some cases, the tooling may be heated to about 30° C., about 40° C., about 50° C., to about 75° C., to about 100° C., to about 125° C., to about 150° C., to about 175° C., to about 200° C., to about 225° C., to about 250° C., to about 275° C., to about 300° C., or higher. Superheat may affect the thickness of the resulting surface modified layer.

[0087] When the slurry-coated tooling comes in contact with molten copper alloy it may cause a phase change (e.g., melting) of one or more of the components of the slurry. In some cases, contact between the slurry-coated tooling and molten copper alloy followed by melting and / or dissolution of metal powder in the slurry. In some cases, contacting the slurry-coated tooling and molten copper alloy is followed by dissolution and / or mixing and diffusion of one or more of the components of the slurry into the molten copper alloy. In some cases, the dissolution and / or mixing and diffusion is confined to less than about 10 mm, about 9 mm, about 8 mm, about 7 mm, about 6 mm, about 5 mm, about 4 mm, about 3 mm, about 2 mm, about 1 mm, about 0.5 mm, about 0.2 mm, about 0.1 mm, or about 0.05 mm from the surface of the resulting copper alloy article. In some cases, the contact between the slurry-coated tooling with molten copper alloy forms a composite. Forming a composite may result from the interaction of the heat of the molten copper alloy with the components of the slurry to transform (e.g., by melting, by dissolution). In some cases, a metal component of the slurry may melt or dissolve, mix and diffuse. In some cases, when the slurry contains a nickel-coated component (e.g., Ni-coated graphite, Ni-coated SiC, Ni-coated Al2O3), the nickel coating may dissolve. In some cases, forming a composite may include transferring ceramic particles in the slurry coating to a surface layer of the resulting copper alloy article, forming a surface composited layer.

[0088] The methods disclosed herein further include solidifying the molten copper alloy and surface modified layer. Forming the surface modified layer can include solidifying the copper-based alloy. Solidifying the copper-based alloy includes cooling the molten copper-based alloy to a temperature below the melting point of the copper-based alloy. In some cases, solidifying the copper-based alloy includes cooling the copper-based alloy to a temperature below about 1300° C., below about 1200° C., or below about 1000° C. Cooling the molten copper-based alloy may include removing a source of heat. Cooling may include conduction, convection, or radiation of heat from the copper-based alloy and / or tooling. These mechanisms of heat extraction may occur concurrently for the cooling of the molten copper-based alloy.

[0089] The advantages of the surface alloyed layer are multifold. In some cases, the properties of the surface alloyed layer are tailorable based upon the composition, viscosity, preheating, and thickness of the slurry layer or layers applied to the tooling, the melt temperature of the molten brass, and the tooling temperature. More specifically, the properties of the surface alloyed / surface composited (SASC) layers depend on the metallic alloying materials (e.g., Cu, Ni, Bi, Sn, etc), type of ceramic or non-metallic particles (e.g., SiC, Al2O3, graphite, etc), and the ratio in which the metallic alloying materials and non-metallic or ceramic particles are mixed or the thickness of the slurry that is applied on the tooling. In some cases, the viscosity of the slurry is important for the application of the slurry to a surface, but the primary effect on the surface alloyed layer's properties is driven by the materials present in the surface alloyed layer. In some cases, the surface alloyed layer improves the corrosion resistance, wear resistance, leaching resistance, and / or oxidation resistance and machinability of the brass component while eliminating or reducing the need for lead or bismuth in the alloy and maintaining machinability. The enrichment of surface of the castings with a surface alloyed layer may also reduce the leaching of undesirable or harmful elements in contact with water. The incorporation of graphite on surfaces of brass castings can impart machinability to castings without use of lead or bismuth additions and can reduce corrosion and leaching of undesirable or harmful elements in water.

[0090] The methods disclosed herein can reduce costs compared to conventional methods for creating surface alloyed / surface composited layers, such as thermal spray, electroplating, laser surface alloying, or vacuum-based coating (e.g., vacuum deposition), by maintaining compatibility with existing casting techniques. Furthermore, because only the surface may be enriched, the bulk copper alloy composition remains largely unchanged, thus preserving the beneficial properties of brass while enhancing its corrosion resistance, leaching resistance, wear resistance, oxidation resistance, and / or machinability at critical surface regions. The surface alloyed / surface composited castings of this work conserve expensive alloying elements, like nickel, copper, and bismuth, to surface layers because, at least in some examples, they are incorporated only near the surface in comparison to through section full thickness. In comparison to full-thickness alloyed castings, where the expensive alloying elements are present all through the cross section, the methods described herein can offer significant reduction in alloying elements, resulting in cost savings.Articles

[0091] Disclosed herein are corrosion-resistant, oxidation resistant, wear resistant, and leaching resistant articles including a cast copper alloy component and a surface modified layer disposed on a surface of the cast copper alloy component. In some cases, the cast copper alloy component includes yellow brass, red brass, bronze, or any combinations thereof.

[0092] The articles disclosed herein define an interior surface and an exterior surface. In some instances, the interior surface defines a cavity or a passageway through the article. In some cases, the interior surface and the exterior surface each include the surface modified layer. In some cases, the interior surface includes the surface modified layer. In other cases, the exterior surface includes the surface modified layer.

[0093] The articles disclosed herein may include articles cast from a copper-based alloy. For example, the article may include a valve or other flow-control components (e.g., butterfly valve, check valve, ball valve, gate valve, globe valve, pressure-reducing valve, backflow preventer, foot valve, solenoid valve body, diverter valve, tubes or pipes), plumbing, piping, and / or pumping components (e.g, fitting (e.g., a pipe fitting), elbow, tee, coupling, union, adapter, hose bibb, faucet body, faucet cartridge, mixing valve body, manifold block, water meter body, pump impeller, pump housing, suction diffuser, basket strainer, Y-strainer), HVAC and / or refrigeration components (e.g., a refrigeration valve body, expansion valve body, compressor fitting), marine hardware (e.g., propeller hubs, sea strainer, pump housings, thru-hull fitting, marine pump component, deck hardware, or propeller hub), industrial and instrumentation components (e.g., pressure gauge housing, flowmeter body, electric connector housing, cable-gland body, switch housing, fuse block), fire protection components (e.g., sprinkler head, sprinkler valve body, fire nozzle body), mechanical hardware (e.g., gear (low-stress), bushing, bearing shell, hinge component, lock body, door hardware), or decorative or architectural articles (e.g., door handle, door knob, door pull, lighting fixture, lamp base, ornamental casting, clock component).

[0094] In some cases, the surface modified layer is a surface alloyed layer, a surface composited layer, or a combination thereof. The surface modified layer can include a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof. More specifically, the surface modified layer may include Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof. In some cases, the metal-coated materials may be coated with nickel or copper (e.g., Ni-coated graphite, Ni-coated Al2O3, Ni-coated SiC, Cu-coated graphite, Cu-coated Al2O3, Cu-coated SiC).

[0095] In some cases, the surface modified layer includes a metal. Examples of metals may include Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Al, Ga, In, Sn, Tl, Pb, Bi, Po, or any combinations thereof.

[0096] In some cases, the surface modified layer includes a metallic alloy. Examples of metallic alloys may include Cu—Sn, Cu—Zn, Cu—Ni, Cu—Al, Cu—Be, Cu—Si, Cu—Mn, Cu—P, Ni—Cr, Ni—Fe, Ni—Mo, Ni—Cu, Ni—Co, Ni—Ti, Fe—C, Fe—Cr, Fe—Cr—Ni, Fe—Mn, Fe—Si, Fe—Ni, Fe—Mo, Fe—W, Al—Si, Al—Mg, Al—Cu, Al—Zn, Al—Mn, Al—Li, Mg—Al, Mg—Zn, Mg—Mn, Mg—Y, Mg—Gd, Ti—Al, Ti—V—Al, Ti—Nb, Ti—Mo, Co—Cr, Co—Cr—Mo, Zn—Al, Zn—Cu, Zn—Mg, or any combinations thereof.

[0097] In some cases, the surface modified layer includes a carbon-containing compound. Examples of carbon-containing compounds include diamond, graphite, amorphous carbon, lonsdaleite (hexagonal diamond), fullerenes (c60, c70, etc.), carbon nanotubes (single-walled, multi-walled), graphene, graphene oxide, reduced graphene oxide, activated carbon, glassy carbon, carbon black, soot, charcoal, coke (petroleum coke, metallurgical coke), nanofoam carbon, q-carbon, carbyne, amorphous diamond (tetrahedral amorphous carbon), turbostratic carbon, or any combinations thereof. In some cases, the carbon-containing compound may include a metal coating. In some cases, the metal coating may include copper, nickel, or any combination thereof.

[0098] In some cases, the surface modified layer includes a ceramic. In some cases, the ceramic includes oxides (e.g., Al2O3, ZrO2, SiO2, MgO, CaO, HfO2, ThO2, BeO, ZnO, TiO2, Cr2O3, spinels, perovskites, mullite, cordierite, zircon, magnesium silicates), carbides (e.g. SiC, WC, B4C, TiC, TaC, NbC, VC, HfC, Cr3C2), nitrides (e.g., Si3N4, AlN, BN, TiN, ZrN, HAN, CrN), oxynitrides (e.g., SiAlON, AlON), borides (e.g., TiB2, ZrB2, HfB2, CrB2), silicides (e.g., MoSi2, WSi2, TiSi2, CrSi2), refractory silicates & phyllosilicates (e.g., Al2Si2O5(OH)4, Mg3Si4O10(OH)2, Al2Si4O10(OH)2, montmorillonite / bentonite clays), and any combinations thereof.

[0099] In some cases, the surface modified layer includes a solid lubricating material. Examples of solid lubricating materials include graphite, molybdenum disulfide, tungsten disulfide, hexagonal boron nitride (h-BN), Pb, Sn, Ni, In, lead oxide, bismuth oxide, copper oxide, silicon nitride, silver-based lubricating phases, barium fluoride, calcium fluoride, or any combinations thereof.

[0100] In some cases, the transition between the surface modified layer of an article and the bulk material of the article is a sharp interface (i.e., there is a clear boundary between the surface modified layer and the underlying bulk metal). In other cases, the transition between the surface modified layer of an article and the bulk material of the article is gradual (i.e., there is no clear delineation between the surface modified layer and the underlying bulk metal).

[0101] In another aspect, the surface modified layer has a thickness, as measured from the surface of the copper alloy article. In some cases, the thickness ranges from about 1 μm to about 5 mm, from about 0.1 μm to about 5 mm, from about 1 μm to about 5 mm, from about 1 μm to about 2000 μm, from about 200 μm to about 1500 μm, or from about 350 μm to about 1500 μm. In some cases, the surface modified layer may have a thickness of about 10 nm to about 10,000 μm. In various instances, surface modified layers may have a thickness of about 100 nm to about 10,000 μm. In various instances, surface modified layers may have a thickness of about 1 μm to 10,000 μm; 25 μm to 5,000 μm; 50 μm to 2,500 μm; or 100 μm to 1,000 μm. In various instances, surface modified layers may have a thickness of no greater than 10,000 μm; no greater than 9,000 μm; no greater than 8,000 μm; no greater than 7,000 μm; no greater than 6,000 μm; no greater than 5,000 μm; no greater than 4,000 μm; no greater than 3,000 μm; no greater than 2,000 μm; or no greater than 1,000 μm. In various instances, surface modified layers may have a thickness of no less than 10 nm; no less than 100 nm; no less than 1 μm; no less than 10 μm; no less than 20 μm; no less than 30 μm; no less than 40 μm; no less than 50 μm; no less than 60 μm; no less than 70 μm; no less than 80 μm; no less than 90 μm; or no less than 100 μm.

[0102] The composition of the surface modified layer of the articles disclosed herein varies with the composition of the slurry containing surface modifying materials used in manufacturing the articles. It may also depend on the composition of the base copper-based alloy used to form the bulk of the article. Tables 4-7 in Example 1 offer exemplary compositions of the surface modified layer as well as the underlying base (a copper based alloy).

[0103] In some cases, the surface modified layer includes oxygen, aluminum, nickel, copper, zinc, tin, bismuth, silicon, and any combinations thereof. Other elements may also be present in the surface modified layer. The surface modified layer may include elements present in the surface modifying material. For example, in cases where the surface modifying material includes Al2O3, the surface modified layer may include aluminum and oxygen. The surface modified layer may include about 6 wt % to about 12 wt % oxygen. The surface modified layer may include about 0 wt % to about 20 wt % aluminum, or about 12 wt % to about 20 wt % aluminum. The surface modified layer may include about 8 wt % to about 17 wt % nickel. The surface modified layer may include about 50 wt % to about 75 wt % copper. In some cases, the copper content of the surface modified layer may be high due to copper in the base copper alloy melt and / or copper particles in the slurry. The surface modified layer may include about 2 wt % to about 20 wt % zinc. The surface modified layer may include about 2 wt % to about 4 wt % Sn. The surface modified layer may include about 0 wt % to about 3 wt % bismuth. The surface modified layer may include about 0 wt % to about 9.0 wt % silicon, or about 3 wt % to about 9.0 wt % silicon.

[0104] As compared to the underlying copper-based alloy, the surface modified layer may be enriched in one or more components present in the slurry containing surface modifying materials used in manufacturing the articles. For example, the surface modified layer may be enriched in oxygen, aluminum, nickel, carbon, silicon, bismuth, or any combination thereof. In some cases, the ratio of the weight percent of an enriched element in the surface compared to the weight percent of the same element in the base copper-based alloy is above about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, or substantially infinite in the case where the surface-enriched element is not present in the base copper-based alloy.

[0105] In some cases, the surface modified layer may be depleted (i.e., have a reduced amount) in one or more components present in the copper-based alloy used to manufacture the articles. For example, the surface modified layer may be depleted in copper, zinc, tin, bismuth, or any combination thereof, as compared to the composition of the copper-based alloy used to manufacture the articles. In some cases, the ratio of the weight percent of a depleted element in the surface compared to the weight percent of the same element in the base copper-based alloy is below about 1, about 0.9, about 0.8, about 0.7, about 0.6, about 0.5, about 0.4, about 0.3, about 0.2, or about 0.1 or less.

[0106] In some cases, the corrosion rate of the corrosion resistant article is reduced by about 20% to about 95%, from about 45% to about 90%, as compared to the corrosion rate of the cast copper alloy component. In some cases, the corrosion-resistance article comprises a reduced leach rate of one or more elements into water, as compared to the leach rate of one or more elements into water of the cast copper alloy component.

[0107] The structure and composition of the surface modified layers on copper alloy articles disclosed herein are unique from the surface alloyed layers or surface composited layers formed by established methods of surface alloying and / or compositing, including laser surface alloying, electroplating, and gas-based surface alloying (e.g., carburizing or nitriding). This is because, for example, the conditions of formation of surface modified layers during the casting process of the disclosed technology are different than the conditions of formation of surface alloyed layers and surface composited layers formed by established processes. Additionally, established methods of surface alloying are significantly more expensive and, in some cases, can only produce a surface modified layer in regions of copper alloy articles which have a line of sight (e.g., an optically unobstructed path from a laser to a region of the copper alloy article). This is not a limitation of the methods and articles disclosed herein.

[0108] The methods and articles disclosed herein have several advantages over existing techniques. For example, surface alloying or surface compositing using the example processes described herein use less alloy material and result in lower costs compared to alloying the components throughout the cross section to improve their surface properties. Likewise, surface compositing using the example processes disclosed herein result in lower cost compared to adding particles or fibers throughout the cross section by utilizing less materials as compared to alloying or compositing the component throughout the entire cross section of the component.Example Embodiments

[0109] Embodiment 1: A low-cost method of producing a cast copper-based alloy component having an enriched, corrosion-resistant and wear-resistant surface, the method comprising:

[0110] (a) providing a copper-based alloy selected from the group consisting of yellow brass and red brass;

[0111] (b) preparing a slurry comprising:

[0112] at least one powder selected from the group consisting of Cu, Ni, Cu—Ni, Cu—Sn, Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and Ni-coated SiC; and

[0113] a binder medium selected from the group consisting of water-based or alcohol-based binders, or superplasticizer;

[0114] (c) coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold; optionally repeating coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold;

[0115] (d) heating the copper-based alloy to a temperature in the range of 1200° C. to 1300° C. or higher;

[0116] (e) pouring the molten copper-based alloy into the coated or mold optionally containing a slurry-coated core, whereby at least part of the powder interacts with the molten copper-based alloy at the surface; or the ceramic particle like graphite, alumina and silicon carbide in the slurry are incorporated in the surface of the casting forming a surface composited layer; and

[0117] (f) solidifying the copper-based alloy to produce a cast component having a surface alloyed layer that is chemically distinct from the bulk alloy and enriched in the elements provided by the powder and / or enriched in ceramic particles like graphite, silicon carbide, alumina or other ceramic or solid lubricating particles incorporated in the slurry and get transferred on the surface of the castings. The melt is poured in the mold in which the core is placed.

[0118] Embodiment 2: The method of embodiment 1, wherein the at least one powder comprises a mixture of copper and nickel powders in a ratio of about a 1:1 ratio to enrich the surface in nickel, thereby improving corrosion resistance in chlorine- or chloramine-rich environments.

[0119] Embodiment 3: The method of any one of embodiments 1 or 2, wherein the at least one powder further comprises bismuth (Bi) powder or a bismuth alloy to increase the bismuth content at the surface of the component, thereby enhancing surface-level machinability and chip formation, without the need of adding bismuth throughout the cross-section.

[0120] Embodiment 4: The method of any one of embodiments 1-3, wherein the at least one powder further comprises nickel-coated graphite powder, forming a surface composite with graphite inclusions that facilitate chip formation and improve machinability and reduce leaching of harmful elements into the water in contact with the castings during their use.

[0121] Embodiment 5: The method of any one of embodiments 1-4, wherein lead (Pb) is supplemented at the surface with or without a combination of bismuth (Bi) and uncoated or nickel-coated graphite, thereby eliminating or reducing the need for incorporating lead through the cross-section as in leaded brass alloys while improving machinability.

[0122] Embodiment 6: The method of any one of embodiments 1-5, wherein at least one powder comprises Cu—Sn powder to lower the zinc (Zn) concentration at the cast component surface, thereby enhancing corrosion resistance in aqueous environments.

[0123] Embodiment 7: The method of any one of embodiments 1-6, wherein the binder medium comprises polyvinyl alcohol (PVA) in about 4 wt % to about 8 wt %, diluted in water, to adhere the powder onto the core or mold surface.

[0124] Embodiment 8: The method of any one of embodiments 1-7, wherein the binder medium is selected from the group consisting of PVA, modified Refcobar 1010, modified Vibrantz, superplasticizer, or any combination thereof.

[0125] Embodiment 9: The method of any one of embodiments 1-8, wherein the slurry includes a plurality of powders selected from the group consisting of Cu, Ni, Cu—Sn (90Cu-10Sn), Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and uncoated or Ni-coated SiC or other powders, in order to form a composite or alloyed layer at the cast surface.

[0126] Embodiment 10: The method of any one of embodiments 1-9, wherein the slurry application is performed selectively on specific areas of the sand core or mold to produce localized regions of different surface chemistries on the cast component, tailored to the corrosive environment or application requirements or abrasive environment.

[0127] Embodiment 11: The method of any one of embodiments 1-10, wherein the thickness of the surface alloyed or composite layer is controlled by varying the amount of the powder or ceramic particles or the number of slurry coats applied to the core or mold.

[0128] Embodiment 12: The method of any one of embodiments 1-11, wherein the powders have particle sizes selected from the group consisting of about 149 μm for Ni, about 74 μm for Cu, about 74 μm for Cu—Sn, about 149 μm for Al, and about 36.5 μm for Ni-coated graphite.

[0129] Embodiment 13: The method of any one of embodiments 1-12, wherein the purity of the at least one powder is between about 95% and about 99.9%.

[0130] Embodiment 14: The method of any one of embodiments 1-13, further comprising pre-heating the coated core or mold at about 100° C. to about 400° C. for about 20 minutes to about 60 minutes or more to remove volatile components from the binder and reduce porosity in the surface alloyed layer.

[0131] Embodiment 15: The method of any one of embodiments 1-13, wherein the slurry-coated core or mold is dried at room temperature of about 20° C. to 25° C., or higher, overnight or longer, thus removing enough volatile content from the binder to mitigate porosity in the resulting surface alloyed layer.

[0132] Embodiment 16: An oxidation-resistant article comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0133] Embodiment 17: A wear-resistant article comprising a cast copper alloy component with a surface alloyed or a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0134] Embodiment 18: A lead leaching resistant article comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0135] Embodiment 19: An article with improved surface machinability comprising a cast copper alloy component with a surface alloyed or surface composited surface layer formed on the exterior and / or interior surface of the cast copper alloy component made by the method of Embodiment 1.

[0136] Embodiment 20: The method of Embodiment 1, wherein the particle size of Ni powder can be in the range of 50 μm to 175 μm, the particle size of Al powder can be in the range of 50 μm to 100 μm, the particle size of Cu powder can be in the range of 50 μm to 100 μm, the particle size of Bi powder can be in the range of 10 μm to 170 μm, the particle size of Cu—Sn powder can be in the range of 50 μm to 100 μm, the particle size of metal-coated Al2O3 powder can be in the range of 50 μm to 250 μm, the particle size of metal-coated graphite powder can be in the range of 16 μm to 200 μm and the particle size of metal-coated SiC powder can be in the range of 10 μm to 100 μm, and the powders are used to prepare the slurry applied on the mold and / or the core surface, as per Embodiment 1.

[0137] Embodiment 21: The copper alloy component can be cast to form a surface alloyed or surface alloyed composited layer with the addition of metal-coated graphite, metal-coated Al2O3 or metal-coated SiC or uncoated graphite, Al2O3 or uncoated SiC or other ceramic particles not mentioned in this literature or a combination thereof particles to the slurry.Miscellaneous

[0138] In the above detailed description, reference is made to the accompanying examples, appendices and drawings in which specific examples are shown by way of illustration. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the disclosure. It should be understood, however, that the detailed description and the specific examples, while indicating examples of embodiments of the disclosure, are given by way of illustration only and not by way of limitation. From this disclosure, various substitutions, modifications, additions rearrangements, or combinations thereof within the scope of the disclosure may be made and will become apparent to those of ordinary skill in the art.

[0139] Unless otherwise indicated, the various features illustrated in the drawings may not be drawn to scale. The illustrations presented herein are not necessarily intended to be actual views of any particular method, device, or system, but are merely idealized representations that are employed to describe various embodiments of the disclosure. Accordingly, the dimensions of the various features as illustrated may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., device) or method. In addition, like reference numerals may be used to denote like features throughout the specification and figures.

[0140] It should be understood that any reference to an element herein using a designation such as “first,”“second,” and so forth does not limit the quantity or order of those elements, unless such limitation is explicitly stated. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements.

[0141] Unless otherwise specified or indicated by context, the terms “a,”“an,” and “the” mean “one or more.” As used herein, unless otherwise limited or defined, “or” indicates a non-exclusive list of components or operations that can be present in any variety of combinations, rather than an exclusive list of components that can be present only as alternatives to each other. For example, a list of “A, B, or C” indicates options of: A; B; C; A and B; A and C; B and C; and A, B, and C. Correspondingly, the term “or” as used herein is intended to indicate exclusive alternatives only when preceded by terms of exclusivity, such as “only one of,” or “exactly one of.” For example, a list of “only one of A, B, or C” indicates options of: A, but not B and C; B, but not A and C; and C, but not A and B. In contrast, a list preceded by “one or more” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of any or all of the listed elements. For example, the phrases “one or more of A, B, or C” and “at least one of A, B, or C” indicate options of: one or more A; one or more B; one or more C; one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C. Similarly, a list preceded by “a plurality of” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of each of multiple of the listed elements. For example, the phrases “a plurality of A, B, or C” and “two or more of A, B, or C” indicate options of: one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C.

[0142] As used herein, “about,”“approximately,”“substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of these terms which are not clear to persons of ordinary skill in the art given the context in which they are used, “about” and “approximately” will mean plus or minus ≤10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.

[0143] As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising” in that these latter terms are “open” transitional terms that do not limit claims only to the recited elements succeeding these transitional terms. The term “consisting of,” while encompassed by the term “comprising,” should be interpreted as a “closed” transitional term that limits claims only to the recited elements succeeding this transitional term. The term “consisting essentially of,” while encompassed by the term “comprising,” should be interpreted as a “partially closed” transitional term which permits additional elements succeeding this transitional term, but only if those additional elements do not materially affect the basic and novel characteristics of the claim.

[0144] Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”

[0145] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0146] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0147] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0148] Other examples and uses of the disclosed technology will be apparent to those having ordinary skill in the art upon consideration of the specification and practice of the invention disclosed herein. The specification and examples given should be considered exemplary only, and it is contemplated that the appended claims will cover any other such embodiments or modifications as fall within the true scope of the invention.

[0149] The Abstract accompanying this specification is provided to enable the United States Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure and in no way intended for defining, determining, or limiting the present invention or any of its embodiments.EXAMPLESExample 1: Surface Alloying and Surface Compositing of a Brass Alloy Castings Using Mold and Core Coatings

[0150] This work presents a low-cost casting process for surface alloyed surface compositing (SASC) of C89836 brass castings. Surfaces of the sand cores were coated with slurries containing varying amounts of Cu, Ni, and reinforcement particles, including Ni-coated Al2O3 and Ni-coated SiC powders, before pouring brass melts into the molds. In SASC samples, Al2O3 and SiC particles were concurrently incorporated into the casting surface, forming a surface composited region. Microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed the formation of a Ni-enriched surface and the successful incorporation of SiC or Al2O3 particles on the casting surface. Electrochemical testing indicated that SASC castings containing Al2O3 and SiC particles exhibited reduced corrosion rates compared to the base alloy. The SA and SASC do not show any delamination when exposed to 250° C. In addition, the size of machining chips was much smaller in SASC, compared to the base alloy. These results demonstrate the potential of SASC as cost-effective routes for producing high-performance surface composited brass components with enhanced corrosion resistance using a single-step casting process.Introduction

[0151] Surface alloying can modify the surface of a base alloy by enriching the surface in Cu, Ni, or Cr to improve wear resistance, hardness, corrosion resistance and resistance to leaching of lead into water. It modifies surface composition and properties near the surface without altering the bulk casting, offering a cost-effective way to enhance performance by selectively alloying surface layers and reducing the need for expensive alloying elements throughout the cross-section of castings. Surface-alloyed components can be used in automotive, aerospace, tooling, and water industry applications. For brass components, surface alloying with Ni, Cr, and B using lasers has improved corrosion resistance; however, laser processing is costly and requires direct line of sight. Researchers have also explored diffusion coating, friction stir processing, and electron beam melting for surface alloying, but all the processes are expensive, require a line of sight, and / or require post-processing.

[0152] Surface alloying can be commercially valuable for brass components used in water systems because it prolongs component life, reduces maintenance costs, and ensures compliance with water safety regulations. Early studies linked chloramine in water to accelerated impingement attack and cavitation; others showed that brass faucets lasted three times longer without chloramine in water. Copper corrosion is strongly pH-dependent, with higher pH reducing chlorine-induced leaching. Later work suggested corrosion begins with oxidative attack by free chlorine, followed by dissolution of products, and is promoted by higher ionic strength, inorganic carbon, and temperature. Diffusion within oxide films slows overall corrosion. Alloying throughout the cross-section, as in Monel or Red Brass, shows superior water-corrosion resistance as compared to yellow brass.

[0153] A prominent corrosion mechanism in brass is dezincification, which involves the selective removal of Zn from the alloy surface exposed to the corrosive medium, resulting in a porous copper structure. This process occurs as Zn is more reactive than Cu and is more easily oxidized and dissolved in water, especially in the presence of slightly acidic or basic conditions. To prevent dezincification in brass alloys, inhibitors such as Arsenic (As) and Tin (Sn) have been added. Arsenic reduces Cu ions to form a protective cuprous oxide layer, while tin creates a film at grain boundaries to inhibit zinc diffusion. Using brass with lower Zn content or applying protective coatings can also help mitigate these corrosion processes. In chloride solutions at 68 F (20 C), α-brasses are prone to dezincification, particularly in stagnant areas and at elevated temperatures, even under flowing conditions. Dezincification is most severe in (α+β) and β-brasses. Brasses containing less than 30 wt % Zn predominantly form the α-phase and thus exhibit greater resistance to dezincification. Taps of red brass and Monel alloys have shown much longer life than yellow brasses, suggesting that higher Ni and Cu contents reduce corrosion. It is anticipated that surface alloying and surface compositing will also reduce dezincification since the surface will be enriched in copper, nickel and ceramic particles.

[0154] Leaching in brass alloys often results in the release of Pb and Cu ions into water, particularly under soft, corrosive conditions. Leaching is most pronounced during the first 24 hours of water stagnation, and regular flushing is an effective way to reduce metal concentrations. Adjusting the pH to around 7.5 or higher, maintaining sufficient alkalinity, and using orthophosphate as a corrosion inhibitor can further reduce lead and copper leaching by forming protective layers on the metal surfaces.

[0155] Lead has traditionally been added to brass to improve machinability by forming discrete particles that act as solid chipbreaks, resulting in smaller chips, smoother surface finish, and reduced tool wear. Even now when lead is not added as a deliberate alloy addition to improve machinability, there is residual lead in the plumbing fixtures due to the use of recycled material, and this can result in a leaching of undesirable amount of lead in water. It is anticipated that surface alloying and surface compositing will also reduce leching of lead in water. There has been considerable work on incorporating hard particles like Al2O3 and SiC through the bulk cross-section of copper alloys using powder metallurgy techniques. Prior research has shown that incorporating ceramic particles, such as Al2O3, into the matrix of copper alloys increases hardness and contributes to high-temperature stability and oxidation resistance. Al2O3 can lead to substantial increases in strength and hardness, for example, the addition of 4 wt % Al2O3 has been shown to cause a 63% increase in hardness and a 136% increase in yield strength, attributed primarily to Orowan strengthening and load transfer. Wear rates of copper alloys decrease by nearly 50% when Al2O3 is incorporated in the matrix of copper alloys. However, its abrasive nature can sometimes lead to higher coefficients of friction, and particle agglomeration can cause pull-out, accelerating wear through “three-body abrasion.” Al2O3 is the preferred reinforcement for increased corrosion resistance of brass alloys due to its dielectric nature and its compatibility with the formation of passive films, thereby enhancing the surface barrier properties. It acts as a physical obstacle, impeding the diffusion of zinc atoms and ingress of chloride ions, thereby mitigating dezincification and decreasing the corrosion rate in aggressive environments. Additionally, Al2O3 is useful for mitigating the release of heavy metals, such as lead (Pb), from brass into drinking water. Al2O3 works by physically covering exposed lead globules that effectively trap the lead. Anodic coatings using aluminum species have demonstrated nearly a 90% reduction in lead leaching.

[0156] Silicon Carbide (SiC) is known for its superior hardness and thermal conductivity compared to alumina. Incorporation of SiC particles in copper alloys leads to extreme abrasion resistance and high load-bearing capability in brass matrices. Incorporation of SiC in the matrix of copper alloys often leads to a low coefficient of friction (COF) in surface nanocomposites. SiC is considered to be a superior reinforcement in copper alloys for tribological applications, shifting the failure mode from severe adhesive wear to mild abrasive wear significantly extending component life. In terms of corrosion properties, SiC is a semiconductor, meaning it can theoretically form micro-galvanic couples with the conductive copper matrix, potentially accelerating the dissolution of the surrounding anodic brass. However, SiC-reinforced copper alloys have been shown to possess superior general corrosion resistance compared to unreinforced alloys.

[0157] Incorporation of SiC or Al2O3 particles throughout the cross sections of copper alloy components to get improved properties is expensive and presents additional challenges in processing of components reinforced throughout the cross section of the castings.

[0158] In this work, a technique for surface alloying and surface compositing of copper alloy sand castings is described, in which Al2O3 or SiC particles can be incorporated near the surface of the castings and alloyed to enrich Nickel and Copper. The technique involves coating molds or cores with slurry containing metal powders such as Ni and Cu (for surface alloying) and Ni-coated alumina and Ni-coated SiC particles (for surface compositing). When molten metal is poured into the mold containing slurry-coated cores on the surface enriched in Ni and Cu (Surface Alloying), Al2O3 or SiC particles are incorporated near the surface (surface compositing) when Ni-coated Al2O3 or Ni-coated SiC particles are present in the slurry. The microstructure, chemical composition, and phases present in the surface alloyed and surface composited layers have been characterized, and improvements in corrosion resistance have been demonstrated. In addition, increase in hardness, adequacy of adhesion between SA and SASC, layers and reduction in size of machining chips has been characterized. This technique represents an improvement over stir mixing and casting, since Al2O3 or SiC, Ni, and Cu are incorporated only near the surface, where they are needed for corrosion resistance, thereby reducing the amounts of Ni, Cu, and alumina or SiC required in through-alloyed and through-composited castings. The surface alloying and surface compositing technique can be readily adopted for sand-cast copper alloy components.Materials and Methods

[0159] Sand cores were coated with slurries containing metallic powders to form an in-situ coating layer on industrial cast components. Each core was coated with two layers of a graphite-based mold and core wash (Technikoat, HA International) to minimize reactions between the molten metal and the core sand, followed by drying under ambient conditions for 24 h. The cores were subsequently coated with a slurry consisting of Ni and Cu powders, Ni-coated Al2O3 or Ni-coated SiC particles, and a water-based binder system comprising either polyvinyl alcohol (PVA) or a combination of PVA and a superplasticizer (Table 1). Nickel was incorporated to enhance corrosion resistance and to reduce potential leaching in Bi-containing brass. The binder was prepared by dissolving PVA powder in water at 80° C. to obtain a 10 wt % solution, after which the metallic powders were incorporated under constant manual stirring to ensure a homogeneous mixture. The metal powders (Ni and Cu) and Ni-coated alumina and SiC particles were measured in quantities shown in Table 1, and the binder was added while maintaining a constant stirring rate. The viscosity of the slurry binder was important, as low viscosity would lead to powder separation. The slurry containing metal powders and Ni-coated alumina and SiC powders was applied on the surface of the cores to form a coating. The coated cores were dried at room temperature for 48 h and then placed into the sand mold. The C89836 alloy melt (at 1200° C.) with the composition listed in Table 2 was subsequently poured into the mold. A schematic illustration of the manufacturing process is presented in FIG. 2.TABLE 1Samples made and the quantities of Ni and Cu powders and Ni-coatedreinforcements used for slurry preparation for coating on cores.Slurry Composition of Core CoatingSampleReinforcementNiCucodeBase alloyBinderReinforcementPowder (g)Powder (g)Powder (g)YBYellow Brass—————S0C89836—————S1C89836PVANi-coatedS2C89836PVA + alumina3.16855SuperplasticizerparticlesS3C89836PVANi-coated SiCS4C89836PVA + particlesSuperplasticizerTABLE 2Elemental composition of base UNS C89836 alloy.ElementCuPbSnZnFePNiAlBiSSbSiMin (%)87.0—4.02.0————1.5———Max (%)91.00.257.04.00.350.060.90.0053.50.080.250.005FIG. 3 shows SEM images of the powders used to make the slurry. FIG. 3 (a)-(d) shows the morphology of the particles, including pure Cu, pure Ni, Ni-coated SiC, and Ni-coated Al2O3, respectively. To show the coating of nickel on Ni-coated powders, they were mounted in epoxy resin using a hot-mounting machine, then ground to a flat surface, and their cross-sections were observed. FIG. 3 (e)-(e3) shows SEM images and elemental mapping of Ni-coated SiC particles, revealing a Ni coating layer with varying thickness. FIG. 3 (f)-(f3) shows the cross-sectional SEM images and elemental mapping of Ni-coated Al2O3 particles, demonstrating a continuous Ni coating on the particle surfaces.

[0161] The castings were sectioned from the SASC regions for metallographic characterization. Samples were cut and mounted in conductive phenolic resin and ground sequentially with SiC abrasive papers of 180-1200 grit. Final polishing was performed using a 1 μm alumina suspension followed by 0.05 μm colloidal silica to obtain a mirror finish. The polished samples were etched with Copper No. 2 (15 mL FeCl3, 15 mL HCl, 100 mL H2O) to reveal the microstructure. Optical microscopy was conducted using a Nikon EPIPHOT 300 microscope under polarized light, while microstructural features were further examined with a JEOL 6460LV scanning electron microscope (SEM) using backscattered (BSE) and secondary electron (SE) imaging. Phase identification was conducted via XRD using a Bruker D8 Discover system, which was equipped with a Ni filter and Cu target and operated at 40 kV and 40 mA. The machinability test was performed using a sweeping tool with a depth profile of 0.254 mm on the samples to evaluate the chip formation behavior.

[0162] Image analysis was performed in ImageJ using a combination of automatic thresholding and manual selection to calculate the area percentages of phases, the size of reinforcement particles, and the size of select phases. Potentiodynamic polarization testing was performed to characterize the corrosion resistance of the samples. Corrosion tests were performed using a potentiostat (SP-200, BioLogic) with tap water at room temperature, containing an estimated chloramine concentration of approximately 2 ppm, as the electrolyte and an exposed surface area of 0.980 cm2 as the working electrode. The SASC samples and platinum wire mesh were used as the working electrodes and counter electrode, respectively, while Ag / AgCl was used as the reference electrode.Results and Discussion

[0163] The presence of a Ni coating on both SiC and Al2O3 particles promoted the formation of a Ni-enriched surface layer on the cast brass components. This SASC layer improved the corrosion resistance of the castings while reducing overall production costs by forming a thin, in-situ-formed surface layer, instead of adding nickel throughout the cross-section. In addition, incorporating ceramic reinforcements, such as SiC and Al2O3, was expected to further reduce corrosion rates and enhance wear resistance by reducing abrasion. SiC has a density of 3.15 g / cm3 and a hardness between 9-10 on the Mohs scale, while Al2O3 has a density of 3.21 g / cm3 and a hardness of 9 on the Mohs scale. Both reinforcement particles had lower densities and higher hardness than brass alloys. Prior work on copper-ceramic composites has shown that lower-density reinforcement particles, such as graphite, Al2O3, or SiC, tend to agglomerate and float to the top of the melt during stir-casting and solidification. The problem of the flotation of reinforcement particles during stir casting is eliminated using the surface composting process described in this work.

[0164] FIGS. 4 (a) and 4(b) show the optical microstructure of the SiC SASC layer formed in situ as a result of the interaction between the molten brass and the slurry-coated core containing SiC reinforcement in the form of Nickel-coated SiC powder and Nickel and Copper powders. The SiC particles were distributed throughout the SASC layer, forming a localized surface-composite layer rich in nickel and SiC particles. The SiC particles were coated with a Ni layer to improve wetting between the melt and the SiC particles and to help improve the bonding. The Ni powder and the Ni coating on the SiC particles dissolved in the brass melt, thereby enriching the surface composited layer with up to 10.69 wt % Ni, which was significantly higher than the 0.9 wt % Ni originally present in the base alloy. FIG. 4(c) shows the area elemental analysis of the SiC-reinforced SASC layer compared with the base alloy. The Ni content in the SASC layer reaches 10.69 wt %, whereas no measurable Ni is detected in the base alloy. Importantly, the SASC process does not significantly alter the concentrations of other alloying elements, such as Bi and Sn, which remain within approximately the same compositional range in the surface alloyed and surface composited layer as they were in the base alloy. FIG. 4(d) also shows the elemental analysis of the phases present in the SASC layer; the lighter phases are uniformly dispersed Bi-enriched precipitates throughout the SASC layer. The Bi-rich precipitates were also located within the Ni-rich islands and in the matrix. The Bi originally present in the base alloy is also incorporated in the SASC layer.

[0165] Elemental mapping of the SASC layer revealed a high concentration of Ni-rich islands in the region between the SiC and Al2O3 particles (FIG. 4 (e)-(e4) and FIG. 4 (e)-(e4)) apparently, as the base alloy melt comes into contact with the metal-coated ceramic powder slurry, the heat from the molten metal melts the Cu powder in the slurry. Simultaneously, the Ni powder and the Ni-coating on the SiC or Al2O3 particles dissolve in the Cu-rich molten metal solution. The melt at the mold-metal interface becomes enriched in Ni, thereby altering the local composition to a Cu—Ni—Zn alloy. The present solidification hypothesis suggests that the Ni-rich islands are the primary phase to form during solidification in the SASC region of the melt. As the phase grows, the reinforcement particles, SiC or Al2O3, are pushed by the growing phase, leading to the observed concentrations of these particles between Ni-rich islands. The pushing of reinforcement particles between Ni-rich islands was more prominent in samples with SiC, as the particle size was smaller than the Al2O3 particles, and SiC has a lower density than Al2O3. The Ni coating on SiC particles was 60% and 25.7% on Al2O3 particles by weight. Thus, the overall Ni concentration in the SASC layer differed between the samples containing SiC and Al2O3 particles. The ternary phase diagram of the Cu—Ni—Zn system suggests that a phase is formed at the start of solidification, which is a solid solution of Cu—Ni—Zn. As the Ni in the SASC zone is trapped in this solid solution, the remaining melt, now depleted in Ni, solidifies to form a Cu—Zn solution.

[0166] The microstructures of the SASC layer incorporating Al2O3 particles are shown in FIG. 5. FIGS. 5(a) and 5(b) show OM images of the Al2O3 SASC in low and high magnifications, respectively. The bright areas represent the Ni-rich island formed due to the Nickel coating on the Al2O3 particles, as the nickel powder in the slurry. FIG. 5(c) shows the EDS analysis of the SASC layer and the distribution of alloying elements, including Ni added as a powder and due to the use of Ni-coated Al2O3 particles. The concentration of Ni ranges from 9.57 wt % to 14.74 wt % in the SASC layer, compared to 0.66 wt % to 1.96 wt % in the base alloy. A higher Ni wt % in the SASC layer indicated the dissolution and subsequent alloying of Ni from the reinforcement particles with the S0 melt. Although the Ni concentration in the SASC layer was lower than that of Monel alloys, a higher wt % of Ni in the SASC layer (than that of the base alloy) is expected to improve corrosion resistance, including chlorine or chloramine-rich environments. The microstructures showed a Ni-rich layer at the particle periphery. In the Al2O3-incorporated samples, when Ni-coated Al2O3 was incorporated into the SASC layer, a nickel-enriched zone remained around the alumina particles, measuring around 13 μm in thickness. Elemental mapping of the microstructure near the particles revealed a Ni rich layer along the perimeters of the Al2O3 in the SASC layer.

[0167] Microstructural studies revealed that a Ni-depleted zone formed around the Ni-rich islands, observed in both SiC- and Al2O3-reinforced samples. The Ni-depleted zone is the area surrounding the SiC or Al2O3 particles, low in Ni content due to the formation of Ni-rich islands. Reinforcement particles were present only in the SASC layer of both samples, (with no reinforcement particles or Ni enrichment observed in the base alloy below the SASC layer). This suggested that the cooling rate of the melt did not lead to significant flotation of the particles, as the density of the reinforcement particles was lower than that of the melt. The average distance between the SiC particles and the periphery of the Ni-rich islands was approximately in the range of 20-25 μm. This distance also corresponded to the thickness of the Ni-depleted zones surrounding such Ni-rich phases. The size of the SiC particles was approximately 25 μm while that of the Al2O3 particles was approximately 200 μm. Prior work on the solidification of composite materials has shown that the presence of reinforcement particles can restrict the growth of the matrix microstructure, including dendrites. The growth restriction is based on the alloy's cooling rate, as the dendrite size correlates with it.

[0168] FIG. 6(a)-6(b) shows the area fraction composition for Ni-rich islands, reinforcement (Al2O3 or SiC) and Bi precipitates on the SASC layer. The S2 sample showed the highest ceramic particle reinforcement area percentage, around 19%. All samples had Ni-rich islands with an area percentage of around 10-13%. FIG. 6(c)-6(d) shows the average sizes of the Ni-rich islands, reinforcement particles, and Bi precipitates in the SASC layer. The average size of the Ni-rich islands was consistent through the SASC layers of all samples, irrespective of the chemistry of the reinforcement particles. These Ni-rich islands did not contain any reinforcement particles, suggesting that the formation of the phase and its subsequent growth pushed the SiC or Al2O3 particles to regions between Ni-rich islands.

[0169] FIG. 6(b) shows the area percentage of bismuth (Bi) precipitates across the different composite samples. The Ni—Cu+Ni—SiC (PVA) sample has the highest concentration of these Bi precipitates. When the superplasticizer is added to this SiC system, the area fraction of Bi precipitates drops by about half to 0.50%. For the Al2O3 composites, the trend is reversed. The PVA-only sample has 0.48% area containing Bi, which increases to 0.70% when the superplasticizer was used. The precipitation of Bi is favored at the grain boundaries in brass alloys with low wt % of Ni. In the presence of Sn, the precipitation of Sn at the grain boundaries is favored over Bi, which can restrict the sites available for the precipitation of Bi. Prior work suggests that the presence of Sn in the alloy affects the precipitation of Bi at grain boundaries, as Sn preferentially precipitates there, preventing Bi segregation. The samples studied showed nucleation of Bi precipitates within the Ni-rich islands in select instances. As the size of the SiC particles and the wt % of Ni in the alloy increase, the formation of Bi bilayers is favored, as they are the thermodynamically stable and dominant interfacial phase at Ni and Cu grain boundaries.

[0170] The effect of Ni wt % in the SASC layer on the average size of Bi precipitates was observed in FIG. 6(d), where samples with Al2O3 as reinforcement had smaller precipitates than samples with SiC as the reinforcement. The SiC samples had a lower wt % of Ni in the SASC layer than the Al2O3 samples, and the Bi precipitates were observed to preferentially nucleate along the SiC particles. Specifically, the S3 sample has the largest average precipitate size at 5.32 μm2. This size decreases slightly to 4.22 μm2 when the superplasticizer is added to the SiC system. In the S1 and S2 samples, the precipitates remain quite small, measuring 1.13 μm2 for the PVA sample and 1.42 μm2 for the superplasticizer sample.

[0171] In FIG. 7(a), most samples showed a thickness of SASC layers of around 1000 μm, with S4 reaching a maximum thickness of 1284 μm. Prior studies have shown that the thickness of the SASC layer can be a function of the quantity of slurry material applied to the mold or core surface. FIG. 7(b) shows the coverage of the SASC layer, defined as the fraction of the sample length covered by the SASC layer. The S1 sample exhibited nearly complete surface coverage (99.81%). In contrast, the lowest coverage was observed for the S2 sample (68.71%). This trend is consistent with the reduced thickness shown in FIG. 7(a) indicates the formation of a more fragmented composite layer. The periphery of the Al2O3 particles within the SASC layer exhibited a Ni-rich coating, indicating incomplete dissolution of the Ni layer in the melt. In contrast, such features were not observed for the SiC particles. FIG. 7(c) shows the Ni shell thickness, a measurement observed in the S1 and S2 samples containing the Ni-coated Al2O3 particle reinforcement, alongside the Ni-depleted length, a measurement observed in the S3 and S4 samples containing the Ni-coated SiC particle reinforcement. For S1 and S2, a Ni rich layer of approximately 13 μm was observed around the Al2O3 particles. In contrast, the Ni-depleted length, representing the average distance between Ni islands and SiC particles, varied between the SiC-reinforced samples. S3 exhibited a higher depletion length of ~25 μm, while S4 showed a reduction to ~20 μm, indicating a more densely packed distribution of SiC particles around Ni islands. The superplasticizer used in this study, MEGAPOL GUSR-AC, assists the dispersion of particles, in this case Al2O3 and SiC, reducing particle agglomeration and improving the fluidity of the slurry. An increase in particle dispersion had different effects on the Al2O3 and SiC slurries due to differences in their particle size. The large-sized Al2O3 particles, present in a highly fluid medium, were assumed to be highly dispersed over the applied core surface, leading to a thinner SASC layer and a lower coverage % of the formed SASC layer. The smaller SiC particles exhibited the opposite trend, forming a thick SASC layer with higher coverage.

[0172] FIG. 8 shows the average corrosion current density (Icorr) for the cast samples. A higher Icorr corresponds to a higher corrosion rate (i.e., lower corrosion resistance); the comparison directly reflects material performance. The YB (yellow brass) sample exhibits the highest corrosion rate, with an Icorr of approximately 1.33 μA / cm2. In contrast, the S0 sample (red brass) shows a 46% reduction in Icorr, reaching 0.73 μA / cm2. This reduction is associated with a lower dezincification rate in the corrosive environment, resulting in a shallower dezincified layer and, consequently, higher corrosion resistance. This behavior can be attributed to the more negative standard electrode potential of Zn (E=−0.763 V) compared with Cu (E=+0.337 V). The large potential difference promotes the preferential dissolution of Zn in corrosive environments, leading to severe dezincification in Zn-rich alloys such as yellow brass. This finding is also consistent with prior literature showing that red brass has considerably higher corrosion resistance than yellow brass. The coated samples exhibited higher corrosion resistance and lower Icorr, with reductions for S1, S2, S3, and S4 compared to S0, respectively. This can be attributed to the formation of Ni-enriched, approximately 10-13 wt %, for continuous and thick SASC layers on the cast components.

[0173] Comparing the electrochemical potentials of Ni and Cu, Ni exhibits a more negative potential than Cu; therefore, Ni is preferentially oxidized in a corrosive environment. The interaction between Cu and chloride ions can be described by the following reaction:

[0174] The solubility of this product is negligible; therefore, it deposits on the sample surface, forming a porous CuCl film.

[0175] Subsequently, hydrolysis reactions may occur, leading to the formation of an oxide passive Cu2O layer on the Cu surface:

[0176] In the absence of Ni, the adsorption of Cl− accelerates the diffusion of metal ions from the metal / passive film interface toward the film / solution interface. This enhanced diffusion leads to the formation of cation vacancies, which promotes pitting initiation and ultimately results in the breakdown of the oxide passive film. However, in the presence of Ni, Ni atoms dissolved into the SASC layer or Ni-rich islands provide a sufficient supply of Ni that can segregate into the oxide passive film through a solid-state reaction and incorporate into the cation vacancies. This incorporation competes with the injection of Cu cations into the oxide passive layer, thereby diminishing pitting and reducing the corrosion rate of SASC cast components.

[0177] FIG. 9 shows the difference in hardness between the various SASC layer types (S1-S4) and the S0 base alloy (S0). All the SASC layer samples showed an increase in hardness compared to the S0 base alloy, which has a hardness value of 81 HV. The highest Vickers hardness value was for sample S4, at 138 HV. As discussed in prior sections, SiC and Al2O3 have higher hardnesses than the C89836 base alloy and an increase in the hardness of the SASC layer is expected. The incorporation of the particles hinders the deformation of the matrix under loading, transferring the load from the matrix to the reinforcement and thus increasing hardness. This was shown in prior work where incorporation of Aluminum Nitride (AlN) up to 12 wt % in brass alloys led to a 38.57% increase in hardness. Brass composites reinforced with SiC whiskers exhibited a 160% increase in the hardness at 40 vol % reinforcement, but experienced a decrease in hardness following 42 vol % reinforcement. These results show that the presence of reinforcement particles in the SASC layer improved the surface hardness of the castings. The hardness of the Al2O3-containing samples was within a 5% range of the samples with and without superplasticizer. In the samples incorporating SiC, the difference in hardness values was approximately 30% between the sample without superplasticizer (S3) and the sample with superplasticizer (S4). This may be due to the differences in the microstructures of samples S3 and S4. The average size of Ni-rich islands was higher in sample S4, the average size of Bi precipitates was lower for sample S4, and the area % of Bi precipitates was also lower for sample S4.

[0178] FIG. 10 shows the X-ray diffraction used to identify the phases formed in the surface-alloyed / surface-composited layer. SiC peaks and Al2O3 peaks were observed, confirming the incorporation of SiC and Al2O3 particles in the SASC layers. The Ni-rich islands, containing Ni, Cu, and Zn with different stoichiometric compositions including Cu0.95Ni0.05 and Cu2NiZn are identified. Other peaks corresponding to Sn and Bi in the S0 bulk alloy were also present in the XRD pattern as the Bi and Sn0.05Ni0.95 phases. These results confirm the transfer of Al2O3 or SiC particles from the slurry-coated cores to the surfaces of the castings, as well as the enrichment of the casting surfaces with Nickel and other metallic powders present in the slurry.

[0179] FIG. 11 shows optical microscopy images of samples S1 and S3 after performing the qualitative adhesion test of metallic coatings as per ASTM B571. The testing cycle consisted of heating the samples to a set temperature (a) 250° C. and (b) 400° C. and rapidly cooling them via a water quench. Because the composition of the SASC layer differs from that of the base alloy, the coefficient of thermal expansion (CTE) differs. Thus, as the sample was heated and rapidly cooled, the delamination of the SASC layer from the base alloy could occur. Additionally, the heating may affect the interface between the SASC layer and the base alloy. Results of sample S1 show the (FIG. 11, panel a1) as cast condition, (FIG. 11, panel a2) after heating treatment after* 250° C., and (FIG. 11, panel a3) after heating to 400° C. and instantly cooling to room temperature by water quenching. There does not appear to be any visible change in adhesion between the interface of the SASC layer and base alloy layer compared to the as-cast specimen. Results of sample S3 show the (FIG. 11, panel b1) as cast condition, (FIG. 11, panel b2) heating to 250° C. followed by quenching, and (FIG. 11, panel b3) heating to 400° C. followed by quenching. Between the 250° C. and 400° C. heat treatment images, there are no visible alterations between the interface of the SASC layer and base alloy layer compared to the as-cast specimen. Porosity present in FIGS. 11(b1) and 11(b3) is present at alternating times between polishing processes of the samples.

[0180] FIG. 12 compares chips collected during machining of four copper-based samples including 12(a) yellow brass, 12(b) base alloy C89836, 12(c) C89836+SA Layer, and 12(d) C89836+SASC layer (Ni—Al2O3). A drill bit was swept across each surface at a cutting depth of 0.010 in so that only the SA or SASC layer was machined. Optical images are shown for Yellow Brass 12(a), C89836 alloy 12(b), Ni—Cu SA layer 12(c), and sample S1 SASC layer with Al2O3 particles 12(d). Machining of Yellow Brass 12(a) produced long, continuous ribbons, reflecting high ductility and poor chip breakage, making it difficult to machine. C89836 alloy 12(b) formed shorter, more fragmented chips, an effect attributed to bismuth additions that aid chip breakage. In contrast, the chips in SA layer were smaller than C89836 alloy and the S1 SASC layer with Al2O3 particles 12(d) lead to the formation of the smallest and most granular chips, consisting of short segments and fine particles. This suggests that Al2O3 particles act as chip breakers, resulting in smaller chips. Overall, chip size decreased progressively from Yellow Brass to C89836, to Ni—Cu SA, and finally to S1 SASC, demonstrating a clear trend toward smaller and more granular chips.

[0181] The results show that smaller machining chips generally achieved by adding Pb or Bi to copper alloys may be achieved by incorporating Ni and Al2O3 into a SASC layer. This may provide a path to replace toxic and expensive alloying elements like Pb and Bi with a low-cost and safer alternative.CONCLUSIONS

[0182] A one-step casting process was developed to synthesize functionally graded surface alloyed (SA) and surface alloyed and surface composited (SASC) C89836 brass castings. This was achieved by coating sand cores with slurries of Ni and Cu powders combined with Ni-coated Al2O3 or Ni-coated SiC powders and then placing them in the mold prior to pouring molten copper alloy.

[0183] The SASC layers successfully formed on the surface of the cast brass components using this process.

[0184] When slurry-coated cores were incorporated in the mold prior to pouring the molten alloy, the interior surface of the castings was successfully surface alloyed and surface composited.

[0185] Optical and electron microscopy studies showed that the surface alloyed and surface composited layers in the surface of the castings were enriched with nickel and copper, and they had significant volume percentages of Al2O3 or SiC particles incorporated in the SASC layers.

[0186] The SASC layers containing Ni, Al2O3 or SiC particles exhibited higher hardness due to the successful incorporation of the SiC and Al2O3 ceramic particles into the matrix.

[0187] The copper alloy castings with SASC surface layer showed reduced corrosion rates compared to the base copper alloy. These castings are also likely to exhibit reduced leaching rates of harmful elements in water.Supporting InformationTABLE 4Bulk Composition of Ni-Al2O3 SASC with PVA from EDS AnalysisComposition(wt %)OAlNiCuZnSnBiSurface8.85 ± 2.6716.06 ± 3.7614.74 ± 1.78 55.03 ± 4.18 3.04 ± 0.592.29 ± 0.120.00 ± 0.00 Base0.33 ± 0.33 0.00 ± 0.00 0.66 ± 0.6686.23 ± 0.57 4.98 ± 0.394.84 ± 0.112.98 ± 0.14TABLE 5Bulk Composition of Ni-Al2O3 SASC with PVA + Superplasticizer from EDS AnalysisComposition(wt %)OAlNiCuZnSnBiSurface9.06 ± 0.0318.82 ± 0.0112.56 ± 0.94 51.60 ± 0.29 3.18 ± 0.95 3.16 ± 0.14 1.63 ± 0.16 Base0.00 ± 0.00 0.00 ± 0.00 1.09 ± 0.0986.45 ± 0.125.19 ± 0.685.26 ± 0.232.03 ± 0.71TABLE 6Bulk Composition of Ni-SiC SASC with PVA from EDS AnalysisComposition(wt %)CSiNiCuZnSnBiSurface5.54 ± 0.38 4.82 ± 1.77 9.57 ± 1.6272.57 ± 2.16 4.60 ± 0.82 3.73 ± 0.19 1.23 ± 0.47 Base3.86 ± 0.661.54 ± 1.541.96 ± 1.7082.30 ± 1.744.43 ± 0.804.51 ± 0.162.05 ± 0.56TABLE 7Bulk Composition of Ni-SiC SASC with PVA + Superplasticizer from EDS AnalysisComposition(wt %)CSiNiCuZnSnBiSurface6.76 ± 0.298.15 ± 0.2112.91 ± 0.66 63.39 ± 0.64 3.15 ± 0.043.44 ± 0.15 2.19 ± 0.19Base4.80 ± 0.100.00 ± 0.00 1.06 ± 0.5383.48 ± 0.425.36 ± 0.374.34 ± 0.230.96 ± 0.50Example 2: Factors Considered for Creating Alloyed and Composited Surface Layers on BrassIntroductionBrass components in water distribution systems are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from metal leaching.The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure. The proposed surface alloying process significantly enhances the durability of brass components by targeting corrosion reduction at its surface. This process is practical and cost-effective, easily integrated into existing foundries without additional equipment. This process involves casting components in molds and cores coated with a slurry containing alloying element powders, enriching the surfaces with elements such as Nickel, Copper, and Bismuth. This method is capable of surface alloying selected surfaces, including internal surfaces in contact with water, and enhancing corrosion resistance to levels comparable to more expensive materials like red brasses and Monel. The process does not require a line-of-sight of the target surface, allowing for the alloying of interior surfaces of complex castings.This approach offers several example benefits:1. Cost Reduction: By alloying only the surface of brass components, the process reduces the need for expensive alloying elements like nickel and copper, lowering production costs.

[0192] 2. Extended Component Lifespan: Improved corrosion resistance through surface leaching alloying significantly extends the lifespan of brass components, resulting in fewer maintenance disruptions and enhancing water distribution system stability.Feasibility Demonstration

[0193] Both yellow brass and bi-alloy red brass were used as base alloys, which were sand cast and alloying elements such as Cu, Ni, Al, and Cu—Sn were used for enriching selected cast surfaces. It was demonstrated that the incorporation of Ni and Cu—Ni powders in the surface alloyed layers lead to improved corrosion resistance of brass components-85% reduction in the corrosion rate of yellow brass and 70% reduction in the corrosion rate of red brass has been observed. The highest thickness of surface alloyed layers achieved was 2 mm in lab scale experiments, and the average thickness was 400 μm.

[0194] Following the demonstration of the feasibility of the surface alloying process both in the laboratory as well as in castings made on the industry floor, a design of experiments was formulated to identify the optimum process parameters for forming continuous surface alloyed layers. The parameters that were tested included melt temperature in the range of 1100-1200° C., mold temperature in the range of 25-125° C., and the ratio of weight percentages of Nickel and Copper proportional to the binder added to the slurry. It was observed that higher melt and mold temperatures and a ratio of 1:1 for Nickel and Copper powders were suitable for forming continuous surface alloyed layers. The elemental composition of the surface alloyed layer showed enrichment in nickel and copper, and the phases formed in the surface alloyed layer were identified. The improved corrosion resistance of the surface alloyed samples in a chloramine-rich aqueous environment was demonstrated compared to control samples of base alloys. The most suitable compositions for surface alloying were selected for an industrial pour at the Fall River Foundry, where the cores were coated with a slurry-containing metallic powders to form surface alloyed layers in the internal surface of the casting. Polyvinyl alcohol (PVA) was explored as the binder for the slurry instead of sodium polyacrylate and Refcohol to compare its effects on residual porosities. Preliminary results are shown in FIG. 13A-13C.

[0195] Investigations into corrosion on brass faucets showed that they were more durable in the absence of chloramine and that corrosion induced by chlorine was influenced by water pH. Further research showed that corrosion is initiated by the oxidative attack on the brass component's surface, followed by the dissolution of the oxidative products. Factors like ionic concentration and temperature were also found to promote corrosion, and the need for diffusion within the oxide layer acted as a retardant.

[0196] The approach used herein integrates surface alloying directly into the conventional casting process, increasing the weight percentage of Cu, Ni, and other selected elements on selected surfaces of cast water industry components and improving the corrosion resistance of yellow brass components. The higher zinc content in yellow brass makes it more susceptible to dezincification and corrosion, especially in chloride-rich, acidic, or high-temperature environments. By enriching the surface of yellow brass with copper through surface alloying, this work aims to create a red brass-like surface on yellow brass components and increase the corrosion resistance of yellow brass components. This process enhances the overall corrosion resistance of the components, leading to longer lifespans, reduced maintenance, and improved system reliability in the water industry.

[0197] Experiments will be aimed at understanding how varying parameters such as melt temperature, mold temperature, and alloying elements effect the corrosion resistance, hardness, adhesion, continuity, thickness, and as-cast finish of the surface alloyed layer. The slurry containing metal powder / s will be applied to selected surfaces of the molds and cores, and the molten metal will be poured. The variables to be controlled for in the experiments will be melt temperature, mold temperature, and slurry composition. After pouring, samples will be taken by bisecting the cast components through the surface alloyed layer. Samples will then be mounted and polished for surface analysis. The hardness test will be conducted on the surface alloyed layer to estimate the mechanical properties of the coated layer. Image analysis will be used to measure the porosity, the thickness of and the volume percentages of phases in the surface alloyed layer. Corrosion testing will be performed using the potentiodynamic test. The as-cast samples will be conditioned in tap water, as it contains the city-approved limits of chlorine and chloramine, for a period of 24-48 hours. Following this conditioning, the Icorr value of the surface alloyed layer and the base metal (yellow and red brass) will be measured.

[0198] The experiments will have a 4 lbs. melt size, with the melt heated to a maximum temperature of 1200 C. The molds, made using chemically bonded sand, will be coated with the metal powder-binder slurry and dried at room temperature. Further heating in a low-temperature furnace at a maximum temperature of 200 C will be performed under a fume hood in order to eliminate some of the gaseous products formed during the heating of the binder. The metallographic preparation will be done using industry-standard methods, and Cooper No. 2 etchant will be used to etch the base metal while leaving the nickel-enriched surface alloyed layer intact. Clemex Vision and ImageJ will be used for image analysis of the microstructure.

[0199] Advanced characterization methods such as Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM-EDS), and X-ray diffraction (XRD) will be used to quantify the chemical composition and identify the phases formed in the surface alloyed layer, respectively. The adhesion of the surface alloyed layer with the base metal will be estimated using temperature cycling. The as-cast sample will be heated, followed by rapid cooling in water. The effect of this sudden heating and cooling on the interface of the surface alloyed layer and base metal will be observed using microscopy.Contemplated Factors:1. Process optimization: The size and composition of the metal powders, melt temperature, the composition of the binder and ratios of said components will be optimized for the application of the metal-binder slurry on mold and core surfaces to get targeted thickness, continuity of surface alloyed layers with controlled microstructure, composition, and surface roughness to achieve targeted corrosion resistance. Statistical analysis will be done to quantify the increase in corrosion resistance.

[0201] 2. Defects: In order to improve the properties of the surface alloyed layer, the formation of defects will be minimized by optimizing the permeability of the mold, reducing the formation of volatile compounds from the slurry, and introducing venting in the molds or cores. The reduction in defects will be quantified.

[0202] 3. Targeted incorporation of bismuth into the surface alloyed layer by incorporating Bismuth powder with copper and / or nickel powder in the slurry coated on the molds and cores was done. As machining is often done only on the surface, incorporating Bismuth on selected surfaces using surface alloying will improve machinability, lowering the cost by eliminating the need to add Bismuth throughout the cross-section

[0203] 4. Testing the adhesion of the surface alloyed layer with the base metal casting: The surface alloyed casting will be cycled between high and low temperatures in accordance with ASTM standards. The components will undergo selected thermal cycling to confirm that separation does not occur between the surface alloyed layer and the base metal.

[0204] 5. Long-term and accelerated corrosion testing: The corrosion resistance will be tested over longer periods of time using accelerated tests or actual field applications in collaboration with industry partners. The objective will be to ensure the prototypes do not fail while operating in a flowing water environment for long periods, as opposed to static testing.

[0205] 6. Testing of surface alloyed prototypes cast for composition, phase analysis, surface hardness, and corrosion resistance.

[0206] 7. Exploring if as-cast surface alloyed layers can be retained after limited deformation processing in simple shapes to explore the applicability of surface alloying to selected wrought components used in the water industry.

[0207] 8. Optimize the size of metal powders and the composition of the slurry used to achieve surface alloyed layers with targeted thickness, continuity, surface roughness, and corrosion resistance.

[0208] 9. Optimize the microstructure of surface alloyed layers to maximize the corrosion resistance in chlorine and chloramine-rich aqueous environments.

[0209] 10. Optimize the binder medium used in the slurry for suspension of metal powders to reduce the formation of porosity in the surface alloyed layer.

[0210] 11. Incorporate Bismuth as an alloying element to improve the machinability of the surface alloyed layer and to reduce unit cost compared to products with Bismuth alloyed through the cross section.

[0211] 12. Demonstrate the adhesion of the surface alloyed layer to the base metal by subjecting surface alloyed castings to selected temperature cycles.

[0212] 13. Explore reducing wetting and imparting hydrophobicity to surface alloyed layers, especially in the interior of castings by controlling microstructure and roughness, and by incorporating hydrophobic reinforcements into surface alloyed layers.

[0213] 15. Demonstrate the improved corrosion resistance of surface alloyed samples and prototypes in laboratory and industrial environments using simulated tests.Example 3: Development of a Surface Alloying Technique to Enhance Corrosion Resistance in Brass Castings

[0214] This work explores a novel surface alloying technique aimed at improving the corrosion resistance of brass castings, particularly in chlorine-rich or chloramine environments. The proposed method offers a cost-effective approach to selectively alloy vulnerable regions during the casting process, even in areas without direct line of sight. By applying slurry coatings containing binders (modified Refcobar 1010 gel, Sodium Polyacrylate, Polyvinyl Alcohol, or modified Vibrantz binder) mixed with alloying powders (Cu, Ni, Sn, Al) onto cores, in-situ surface alloying was achieved.

[0215] Material Characterization through Optical Microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), hardness measurements, and corrosion analysis. Industrial-scale trials conducted at Fall River Foundry validated the feasibility of this technique. Results demonstrated minimal porosity and distinct alloyed layers, with XRD analysis identifying favorable compositions, including Copper-Nickel-Tin, Copper-Nickel-Zinc, and Copper-Zinc solid solutions. Potentiodynamic corrosion tests demonstrated a significant improvement in corrosion resistance, with copper-alloyed samples exhibiting at least three times the resistance of the base alloy.

[0216] These findings highlight the potential of this surface alloying method to extend the lifespan of brass components, reduce element leaching into water systems, and provide a targeted, scalable solution for corrosion-prone areas in industrial applications.Example 4: Low-Cost Surface Alloying of Copper Alloys Including Brass to Improve Corrosion Resistance in Chlorine and Chloramine Rich Environments

[0217] This work aims to develop the technology of low-cost surface alloying of copper alloy plumbing fixtures during sand casting, to extend the life of components and reduce corrosion and surface damage in water containing chlorine and chloramine.

[0218] The inventors have been able to demonstrate the feasibility of surface alloying of two copper alloys, including yellow brass and Bi-alloy, at the lab scale; slurries containing metal powders were coated on the selected surfaces of molds and cores to achieve surface alloying on inner and outer surfaces of castings. Limited castings have also been made on the industry floor with slurry-coated molds and cores. However, the surface alloyed layers observed in early stage, lab-cast samples were thin (<200 μm) and often had defects and nonuniformities.

[0219] The methods disclosed herein are much cheaper and does not require line of sight as in laser surface alloying and other surface alloying processes; it is also especially suited for surface alloying interior surfaces of castings by coating the slurry on cores that form the internal surfaces. In fact, our process can enable varying degrees of surface alloying on different surfaces of the same casting depending on different exposures to corrosive environments. In addition, the methods disclosed herein enable the use of lower-cost copper alloys in the interior with surface alloyed layers instead of using highly alloyed castings where costly and scarce alloying elements are incorporated throughout the cross sections.

[0220] The inventors' process can be readily implemented by either captive foundries or at foundries that manufacture plumbing castings of copper alloys by coating the surfaces of molds and cores with slurries containing metal powders before pouring the melts in the molds. The inventors will provide the know-how on the selection of metal or alloy powders to be mixed in slurries and the application of slurries on selected surfaces of molds and cores. In addition, the use of surface alloyed components will reduce the amount of metal ions leaching into the water, reducing dezincification and pit formation on the casting surface. For example, enriching the surface of yellow brass in Cu will bring the surface composition closer to red brass, which has higher corrosion resistance. Enriching the surface of red brass with Ni and other elements will further increase their corrosion resistance, which shows much higher life in chloramine environments, at much lower costs. The work aims to improve the corrosion resistance of copper alloys, including brass, in water systems that have chlorine and chloramine. Brass, commonly used in tubing, piping, faucets, and valves, is prone to corrosion and dezincification from free chlorine, including chloramine-derived chlorine. The feasibility of surface alloying of yellow brass and Bi-alloy by sand casting process has been demonstrated on a lab scale where thin surface alloyed layers (<200 μm) were produced on yellow brass and bi-alloy castings; we also were able to demonstrate that castings can be poured with slurry coated on molds and cores in industrial conditions.

[0221] The objective of this work is to improve the surface alloying process to control the thickness, soundness, uniformity, reproducibility, and composition of the surface alloyed layer. The corrosion resistance and material characteristics of the surface-alloyed samples will be compared against standard alloys (yellow brass, red brass, bi-alloy) to determine the effectiveness of the surface alloying process for increasing corrosion resistance. Selected prototypes of plumbing components will be cast on the industry floor, and their enhanced life will be demonstrated in lab-scale corrosion tests and, if possible, under actual service use. Additionally, a techno-economic analysis will be done after optimization of the process to demonstrate the cost savings by using surface alloyed castings with enhanced corrosion resistance, compared to base alloy castings and through alloyed castings.Objectives:1. Control of thickness, uniformity, soundness, reproducibility, and composition of the surface-alloyed layers both in samples and prototypes cast.

[0223] 2. Molds and Cores for selected castings will be coated with powder slurries to produce surface alloyed prototype castings.

[0224] 3. Demonstrate the improvement in corrosion resistance of surface alloyed castings in chlorine and chloramine-rich environments, including resistance to dezincification and pitting.

[0225] 4. Benchmark galvanic corrosion potential of surface alloyed samples to standard commercially-available alloys (recreate galvanic series and incorporate our SA samples)

[0226] Others observed that brass faucets exhibited three times greater durability in the absence of chloramine in water compared to water containing 1 mg / l of chloramine. Earlier work theorized that corrosion is initiated with a direct oxidative attack of the copper surface by free chlorine, followed by the dissolution of the oxidative products from the surface.

[0227] Surface alloying is a surface engineering technique where the outer layer of base material is intentionally enriched in selected alloying elements to a depth of tens to thousands of microns. Methods like carburizing, nitriding, chromizing, and boronizing have been commonly used for surface alloying of steels to enhance specific material properties such as wear and corrosion resistance. Various other surface alloying techniques, including diffusion coating, laser surface alloying, friction stir processing, and electron beam melting, have been explored by researchers for surface alloying. Others' surface-alloyed Brass surface with a Ni—Cr—Si—B powder using a high-power laser, resulting in improved corrosion and erosion resistance. However, these methods are expensive, difficult to scale up, require direct line-of-sight, and often require additional post-processing, leading to increased manufacturing time and costs. The approach disclosed here integrates surface alloying directly into the conventional sand-casting process, with only one additional step of coating the molds and / or cores with a slurry containing alloying elements before pouring the melt into the mold.

[0228] Increasing the weight percentage of certain alloying elements on the surfaces of copper alloy castings will increase their corrosion resistance. For instance, others' high in Ni components lasted 330 days in water containing chloramine, whereas components of red brass and yellow brass lasted 63 days and 14 days respectively, documenting that adding Nickel, Copper and other elements to the surface of these castings, will improve their corrosion resistance. This disclosed research focuses on increasing copper in the surface of yellow brass components, resulting in a composition closer to red brass on the surface while containing yellow brass in the interior bulk. Yellow brass is more susceptible to dezincification due to its higher Zinc content, leading to material degradation, especially in chloride-rich environments. Likewise, the surfaces of red brass and Bi-Alloy, and other alloy castings will be enriched in Ni and other elements to further improve their corrosion resistance.Results

[0229] In initial experiments, commercial binders were used to make slurries for coating molds and cores. Powders of Cu, Ni, Al, and Sn were added to the slurry. The SEM / EDS result, (FIGS. 14(a) and 14(b), shows the microstructure of sample S9, bi-alloy poured in a mold coated with a slurry containing Ni powders, and its EDS analysis showing the change in composition from the surface alloyed layer to base metal (showing enrichment in Ni). Similar results are shown in FIGS. 14(c) and 14(d), where the surface of yellow brass samples was enriched with Cu. FIG. 15(a) shows the samples cast. FIGS. 15(b) and 15(c) show the slurry-coated cores placed in molds and the castings made using this setup, respectively. In some cases, the surface alloyed layers showed porosity and non-uniform thickness etc.

[0230] Contemplated variables including the type of binders; powder sizes and shapes; slurry consistency, and processing parameters, were optimized to increase the thickness, soundness, and uniformity of surface alloyed layers. Quantitative relationships were developed between processing variables and these parameters. Copper alloys, including yellow brass and Bi-alloys were cast.

[0231] The corrosion resistance of surface alloyed layers on both coupons and selected prototypes will be tested using linear polarization, potentiodynamic tests and immersion in mediums containing chlorine and chloramine. The life of surface alloyed components and samples, and corrosion rates, will be tested. Additional tests will be done with both SA and commercial alloys to benchmark the galvanic potential in salt water. This will provide a simple comparative rating using the standard galvanic series as a reference.

[0232] Further contemplated factors:

[0233] 1. The transfer mechanism of alloying elements from the slurry-coated molds and cores to the surface alloyed layer and the solidification of material in the surface alloyed layer will be analyzed. The composition, soundness, reproducibility, thickness, and uniformity of surface alloyed layers enriched in Cu, Ni, Sn, and Al and their combinations will be optimized.

[0234] 2. Corrosion testing samples and prototype castings made in the industry will be done. Dezincification and pitting during corrosion tests will be studied in addition to mass loss from the surface. Prototype surface alloyed samples will be benchmarked to commercial alloys by recreating the galvanic series via corrosion potential measurements in salt water.

[0235] 3. The increase in the life of components as a result of surface alloying will be quantified, and the ability to predict the life of surface alloyed castings will be developed.

[0236] 4. Prototypes will be cast using coated cores for surface alloying of internal surfaces, using bi-alloy and other copper alloys.

[0237] 5. Prototypes will be cast using coated molds for surface alloying of external surfaces using yellow brass.

[0238] 6. Techno-economic analysis of cost savings and increase in profitability as a result of surface alloying technology.Example 5: Surface Alloying of BrassMaterials and Methods

[0239] A total of 64 cores were received and were divided in the format shown in Table 8. Step 1 was to coat all cores with a graphite wash to prevent any reaction between the melt and sand particles. This is a standard practice in the industry. Following the graphite wash, all cores were then manually coated with the corresponding slurry mixtures. Afterward, the coated cores were dried at ambient temperature. This drying process is necessary to ensure the volatile compounds are evaporated before the casting process. This further helps to reduce the formation of porosities. Once dried, the cores were transferred back to the Fall River Foundry and molten metal was poured in the molds containing the cores to make the casting.TABLE 8Copper alloy specimens cast. L = low, H = high, U = uncoated, N = Nickel coated, P = polyvinyl alcohol (PVA), S = superplasticizerSamplewt % ofReinforcementNi-No.BiAl2O3SiCGraphiteBinderReinforcement(g)Cu(g)1LP0.0150.31682.5,2.52LP0.0150.31682.5,2.53LP0.0150.31682.5,2.54LP0.0150.31682.5,2.55LS0.0150.31682.5,2.56LS0.0150.31682.5,2.57LS0.0150.31682.5,2.58LS0.0150.31682.5,2.59HP0.030.63362.5,2.510HP0.030.63362.5,2.511HP0.030.63362.5,2.512HP0.030.63362.5,2.513HS0.030.63362.5,2.514HS0.030.63362.5,2.515HS0.030.63362.5,2.516HS0.030.63362.5,2.517UP0.153.1682.5,2.518UP0.153.1682.5,2.519UP0.153.1682.5,2.520UP0.153.1682.5,2.521US0.153.1682.5,2.522US0.153.1682.5,2.523US0.153.1682.5,2.524US0.153.1682.5,2.525NP0.153.1682.5,2.526NP0.153.1682.5,2.527NP0.153.1682.5,2.528NP0.153.1682.5,2.529NS0.153.1682.5,2.530NS0.153.1682.5,2.531NS0.153.1682.5,2.532NS0.153.1682.5,2.533UP0.153.1682.5,2.534UP0.153.1682.5,2.535UP0.153.1682.5,2.536UP0.153.1682.5,2.537US0.153.1682.5,2.538US0.153.1682.5,2.539US0.153.1682.5,2.540US0.153.1682.5,2.541NP0.153.1682.5,2.542NP0.153.1682.5,2.543NP0.153.1682.5,2.544NP0.153.1682.5,2.545NS0.153.1682.5,2.546NS0.153.1682.5,2.547NS0.153.1682.5,2.548NS0.153.1682.5,2.549UP0.153.1682.5,2.550UP0.153.1682.5,2.551UP0.153.1682.5,2.552UP0.153.1682.5,2.553US0.153.1682.5,2.554US0.153.1682.5,2.555US0.153.1682.5,2.556US0.153.1682.5,2.557NP0.153.1682.5,2.558NP0.153.1682.5,2.559NP0.153.1682.5,2.560NP0.153.1682.5,2.561NS0.153.1682.5,2.562NS0.153.1682.5,2.563NS0.153.1682.5,2.564NS0.153.1682.5,2.5Copper alloy specimens cast. L = low, H = high, U = uncoated, N = Nickelcoated, P = polyvinyl alcohol (PVA), S = superplasticizerSurfaceDesiredLocalLocalNi-SampleAreaThicknessVolumeMasswt % ofReinforcementCuNo.(cm2)(cm)(cm3)(grams)Reinforcement(g)(g)1240.12.421.120.0150.31685, 52240.12.421.120.0150.31685, 53240.12.421.120.0150.31685, 54240.12.421.120.0150.31685, 55240.12.421.120.0150.31685, 56240.12.421.120.0150.31685, 57240.12.421.120.0150.31685, 58240.12.421.120.0150.31685, 59240.12.421.120.030.63365, 510240.12.421.120.030.63365, 511240.12.421.120.030.63365, 512240.12.421.120.030.63365, 513240.12.421.120.030.63365, 514240.12.421.120.030.63365, 515240.12.421.120.030.63365, 516240.12.421.120.030.63365, 517240.12.421.120.153.1685, 518240.12.421.120.153.1685, 519240.12.421.120.153.1685, 520240.12.421.120.153.1685, 521240.12.421.120.153.1685, 522240.12.421.120.153.1685, 523240.12.421.120.153.1685, 524240.12.421.120.153.1685, 525240.12.421.120.153.1685, 526240.12.421.120.153.1685, 527240.12.421.120.153.1685, 528240.12.421.120.153.1685, 529240.12.421.120.153.1685, 530240.12.421.120.153.1685, 531240.12.421.120.153.1685, 532240.12.421.120.153.1685, 533240.12.421.120.153.1685, 534240.12.421.120.153.1685, 535240.12.421.120.153.1685, 536240.12.421.120.153.1685, 537240.12.421.120.153.1685, 538240.12.421.120.153.1685, 539240.12.421.120.153.1685, 540240.12.421.120.153.1685, 541240.12.421.120.153.1685, 542240.12.421.120.153.1685, 543240.12.421.120.153.1685, 544240.12.421.120.153.1685, 545240.12.421.120.153.1685, 546240.12.421.120.153.1685, 547240.12.421.120.153.1685, 548240.12.421.120.153.1685, 549240.12.421.120.153.1685, 550240.12.421.120.153.1685, 551240.12.421.120.153.1685, 552240.12.421.120.153.1685, 553240.12.421.120.153.1685, 554240.12.421.120.153.1685, 555240.12.421.120.153.1685, 556240.12.421.120.153.1685, 557240.12.421.120.153.1685, 558240.12.421.120.153.1685, 559240.12.421.120.153.1685, 560240.12.421.120.153.1685, 561240.12.421.120.153.1685, 562240.12.421.120.153.1685, 563240.12.421.120.153.1685, 564240.12.421.120.153.1685, 5Results and DiscussionOptical Microscopy

[0240] FIG. 16 presents the sample numbers against the highest thickness of the surface-alloyed layer achieved for each specimen cast using the in-mold surface alloying approach. It is evident that the surface-alloyed specimens with Ni-coated SiC, samples 41-48, achieved the thickest surface composited layers. Additionally, the group of castings with Ni-coated SiC proved to be the most successful, with 6 out of 8 samples achieving successful surface compositing. In contrast, the surface-alloyed samples 17-24, with uncoated Al2O3 were unsuccessful, showing no evidence of measurable surface alloy layer formation. A similar trend was observed for uncoated SiC and uncoated graphite samples where no measurable surface composited layer was observed under conditions of present manufacture. The present work indicates that nickel coating facilitates the transfer of graphite and ceramic particles from the slurry to the surface composited layer. It appears that uncoated ceramic particles will require modification in melt composition or pretreatment for them to form a surface composited layer.

[0241] FIG. 17 shows the optical microstructure of all successful samples cast in Fall River, along with their corresponding sample numbers. The depth of surface alloying for all samples has been marked on the micrographs. The greatest thickness of surface alloyed or surface composited layer was observed in sample 44, with a 1190 μm surface-alloyed layer produced using Ni-coated SiC mixed with a PVA binder. It appears that using this PVA as a binder results in better surface-alloyed layers.

[0242] Table 9 presents the quantitative measurements of consistency and porosity of surface-alloying layers and base metal. Based on the data from Table 9 and FIG. 16, the optimal samples in terms of surface-alloying layer thickness, consistency, and low porosity are Samples 41-48, where the cores were coated with Ni-coated SiC. Samples with the highest consistency are indicated in red font. The samples fabricated with superplasticizer achieved the highest thickness of surface alloying, making them superior in terms of alloy layer formation.

[0243] Among these samples, Sample 47 exhibits high consistency and low porosity in both the surface-alloyed or surface composited layer and the base metal, making it an excellent specimen. This result is likely due to the presence of a Ni coating on the graphite layers, which enhances wettability between the molten metal and the slurry. The Ni—Cu phase diagram (FIG. 18) demonstrates the high solubility of Ni in Cu.TABLE 9Quantitative measurements of consistencyof surface alloying layers.Porosity level in Brass Samples 2025SampleSurface alloyednumberConsistency levellayerBase metal1LOWHIGHLOW3LOWHIGHLOW5LOWMEDIUMLOW6MEDIUMMEDIUMLOW7HIGHMEDIUMLOW9LOWHIGHMEDIUM10HIGHMEDIUMLOW11HIGHHIGHHIGH12MEDIUMHIGHLOW15LOWLOWLOW25HIGHLOWMEDIUM26MEDIUMLOWLOW28LOWLOWLOW30MEDIUMLOWLOW31HIGHLOWLOW32LOWLOWLOW41LOWLOWHIGH42MEDIUMMEDIUMHIGH43MEDIUMLOWMEDIUM44HIGHMEDIUMLOW47HIGHLOWLOW48MEDIUMLOWLOW57HIGHMEDIUMMEDIUM58HIGHMEDIUMLOW59HIGHMEDIUMLOW60HIGHMEDIUMHIGH62LOWLOWLOWScanning Electron Microscopy (SEM)

[0244] FIG. 19 shows the scanning electron microscopy (SEM) image of a portion of the surface-alloyed layer of Sample 47. This sample exhibits a surface-composited layer with a homogeneous distribution of Si and Ni. The coating is separated from the surface-alloyed layer by a dashed line.

[0245] Comparing uncoated particle-reinforced surface composite vs coated particle-reinforced surface composites:

[0246] Sample 47 was selected as the optimal Ni-coated particle-reinforced surface composite sample. However, none of the uncoated particle-reinforced surface composited showed measurable amount of ceramic particles in the surfaces (FIG. 16). Among them, samples with a high bismuth content exhibited acceptable consistency with medium level of porosity in the surface-alloyed layer. Table 10 presents a comparison of the highest achieved surface-alloyed layer thickness between Sample 47 and Sample 10.TABLE 10A comparison between of the highest achieved surface-alloyedlayer thickness between Sample 47 and Sample 10.Sample'sHighestConsistencyPorosity level innumberthickness (um)levelcoated layer47818.9HighLow10518.1HighMediumExample 6: Low-Cost Surface Alloying of Yellow Brass to Improve Corrosion Resistance in Chlorine and Chloramine-Rich EnvironmentsTABLE 11Elemental Composition of yellow brass.ElementCuZnAverage (wt %)6040TABLE 12Life of various alloys in chloramine-rich water.AlloyComponent life in chloramineYellow Brass32 daysRed Brass63 daysMonel330 days TABLE 13Elemental composition of Bi-Alloy Brass.ElementCuSnPbZnFeNiAlSiSbSPSeBiMnAverage89.14.460.0204.610.0560.8250.0030.000.0440.0070.0250.0081.700.00(wt %)TABLE 14Elemental composition of Monel 400.ElementCuFeCSiSMnNiMin (wt %)28—————BalanceMax (wt %)342.50.30.50.0242BalanceTABLE 15Alloying powders utilized for the process.Alloying ElementParticle SizePurityCu−200 mesh99%Ni−100 mesh99.9%  Cu—Sn (90 wt %-10 wt %)−200 mesh99%Al 200 mesh99%TABLE 16List of successful experiments conducted.PouringTemper-Sam-AlloyingaturepleElement(C.)AlloyTypeFluxBinderS7Ni>1200Bi-AlloyOpen PourBoraxSodiumPolyacrylateS9Ni>1200Bi-AlloyOpen PourBoraxModifiedRefcobar1010S11Ni>1250Bi-AlloyOpen PourBoraxModifiedRefcobar1010S18Ni1200Bi-AlloyOpen PourBoraxModifiedRefcobar1010S19Ni1100Bi-AlloyOpen PourBoraxModifiedRefcobar1010S20Ni1100Bi-AlloyOpen PourNoModifiedRefcobar1010S27Ni-Al1200YellowOpen PourGlass ModifiedBrassand Vibrantz BoraxTechnologiesS29Cu-Al1200YellowOpen PourGlass ModifiedBrassand Vibrantz BoraxTechnologiesTABLE 17List of samples using yellow brass.SampleAlloying ElementsRatioBinderC0———Modified VibrantzC1Cu——TechnologiesC2Ni——C3CuAl1:1C4NiAl1:1C5Al——C6CuSn9:1C7CuNi1:1C8CuAl3:1C9NiAl3:1C10CuNi3:1TABLE 18List of samples using Bi-Alloy brass.SampleAlloying ElementsRatioBinderB1Cu——Modified RefcobarB2Cu——1010B3Ni——B4Ni——B5CuAl1:1B6CuAl1:1B7CuAl3:1B8CuAl3:1B9NiAl1:1B10NiAl1:1B11NiAl3:1B12NiAl3:1B13Al——B14Al——B15CuSn9:1B16CuSn9:1B17CuNi3:1B18CuNi3:1B19CuNi4:1B20CuNi4:1TABLE 19List of samples made using Bi-Alloy brass.SampleAlloying ElementsRatioBinderO1Cu——Modified VibrantzO2Cu——TechnologiesO3Ni——O4Ni——O5CuAl1:1O6CuAl1:1O7CuAl3:1O8CuAl3:1O9NiAl1:1O10NiAl1:1O11NiAl3:1O12NiAl3:1O13Al——O14Al——O15CuSn9:1O16CuSn9:1O17CuNi3:1O18CuNi3:1O19CuNi4:1O20CuNi4:1TABLE 20List of samples made using Bi-Alloy brassUWMNotationAlloying ElementsRatioBinderNickel-Graphite TrialsP1NiGraphite1:1Modified VibrantzTechnologiesP2NiGraphite1:1Modified Refcobar 1010Sprinkle Trials*P3Ni——Modified VibrantzTechnologiesP4Ni——Modified Refcobar 1010P5CuSn9:1Modified VibrantzTechnologiesP6CuSn9:1Modified Refcobar 1010Control SamplesP7————P8————Extra SamplesP9CuNi1:1Modified VibrantzTechnologiesP10ACu——Modified Refcobar 1010P10BAl——Modified VibrantzTechnologies*Sprinkle Trials: A layer of binder was applied on the core surface, following which alloying powder was sprinkled on the binder. This methodology was implemented to determine whether the alloying powders being mixed with the binder vs. sitting on top of the binder will have any effect on the surface alloyed layer produced.Sample Observations:Sample S9 of Table 16 and FIG. 20-21: The mold was chemically bonded sand. A larger melt volume was used. A distinct surface alloy (SA) layer was observed. There is consistent Ni % in the SA layer. The SA has a uniform thickness. Some porosity was observed still in the cast.TABLE 21Chemical composition of the bulk metal and surface alloyed layerof Sample S9, corresponding to spectrum locations FIG. 22.CNiCuZnSnSpectrum(% wt)(% wt)(% wt)(% wt)(% wt)Spectrum 1 (SA layer)24.2654.2317.364.14Spectrum 2 (SA layer)2.1825.6363.154.025.02Spectrum 3 (bulk)3.8787.923.664.84Spectrum 4 (bulk)4.7690.714.53Sample S18 of Table 16 and FIG. 23: The mold was chemically bonded sand. A continuous SA layer was observed. Ni % in the SA layer was above 20 wt %. Porosity was detected in the casting.TABLE 22Chemical composition of the bulk metal and surfacealloyed layer of Sample S18, correspondingto spectrum locations shown in FIG. 23.NiCuZnSnSpectrum(% wt)(% wt)(% wt)(% wt)Spectrum 1 (SA layer)21.8671.153.003.98Spectrum 2 (SA layer)28.2664.123.584.03Spectrum 3 (bulk)1.6589.473.964.92Spectrum 4 (bulk)1.8189.714.493.98Sample S19 of Table 16: The mold was chemically bonded sand. A very thin surface alloy layer of about 15 μm to about 20 μm was observed. The SA layer was continuous. The Ni % in the SA layer was above 20 wt %. Low porosity was observed in the casting.TABLE 23Chemical composition of the bulk metal and surfacealloyed layer of Sample S19, as shown in FIG. 24.SpectrumNi (% wt)Cu (% wt)Zn (% wt)Sn (% wt)Spectrum 1 (SA layer)48.7812.530.0038.69Spectrum 2 (SA layer)28.5965.411.314.69Spectrum 3 (bulk)1.2492.092.214.46Spectrum 4 (bulk)0.8492.411.804.95Sample S27 of Table 16: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. The Cu % in the SA layer was above 88.45 wt %. No porosity was observed in the casting.TABLE 24Chemical composition of the surface alloyed layer of Sample S27collected at a range of locations in the surface alloy layer.AlCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer, surface-1.4888.4510.07most)Spectrum 2 (SA layer, mid-0.6471.1128.25layer)Spectrum 3 (SA layer, closest0.4163.6235.97to base metal)Sample S27 of Table 16: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. The Cu % in the SA layer was above 80 wt %. No porosity was observed in the casting.TABLE 25Chemical composition of surface alloyed layer of Sample S27collected at a range of locations in the surface alloy layer.AlCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer, surface-0.8190.478.10most)Spectrum 2 (SA layer, mid-1.0469.3628.37layer)Spectrum 3 (SA layer, closest0.0066.0833.43to base metal)Sample C4 of Table 17: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm to about 75 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample C10 of Table 17: The mold was chemically bonded sand. A thin surface alloy layer of about 25 μm to about 50 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B4 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 26Chemical composition of the bulk metaland surface alloyed layer of Sample B4.NiCuZnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer)62.1434.483.38Spectrum 2 (Base Metal)1.0494.404.56Sample B2 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm to about 120 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B3 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 150 μm was observed. The SA layer was discontinuous. Some porosity was observed in the casting.Sample B7 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 75 μm to about 90 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample B10 of Table 18: The mold was chemically bonded sand. A thin surface alloy layer of about 50 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.Sample P3 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm to about 200 μm was observed. The SA layer was discontinuous. Minor porosity was observed in the casting.Sample P5 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 100 μm was observed. The SA layer was discontinuous. Minor porosity was observed in the casting.Sample P9 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 200 μm to about 350 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 27Chemical composition of the bulk metaland surface alloyed layer of Sample P9.NiCuSnSpectrum(% wt)(% wt)(% wt)Spectrum 1 (SA layer)36.6457.026.34Spectrum 2 (SA layer)18.9177.603.49Spectrum 3 (Bulk)—93.626.38Spectrum 4 (Bulk)—95.914.09Example 7: Select Corrosion Testing ResultsSample P9 of Table 20: The mold was chemically bonded sand. A thin surface alloy layer of about 200 μm to about 350 μm was observed. The SA layer was continuous. Minor porosity was observed in the casting.TABLE 28Potentiodynamic corrosion testing results for Bi-alloy base,Sample 22, Sample 28, and Sample P9 (49). A 1 cm2 areawas tested. Each test was duplicated. Counter electrode:Platinum mesh. Reference electrode: Ag / AgCl in 3.5M KCl.Electrolyte: Tap water with about 2 ppm chloramine.SA AlloyingSampleelementE corr (mV vs Ref)I corr (μA)Bi-alloy base1090.714Sample 22Cu950.220Sample 28Cu:Al = 3:1720.227Sample P9 (49)Cu:Ni = 1:1670.249Samples having a surface alloy layer demonstrated about 3× more corrosion resistance than the bi-alloy base.Example 8: Surface Alloying and Surface Compositing of Copper Alloy Castings Using Mold and Core CoatingsThis work presents a technique for simultaneous surface alloying and surface compositing (SASC) of C89836 brass castings. Core surfaces were coated with a slurry of Cu, Ni, and Ni-coated graphite powders before casting. During solidification, Ni and Cu dissolved into the melt and enriched the surface, while graphite particles were embedded in the matrix, forming a composite layer. Microstructural characterization by optical microscopy, SEM, and XRD confirmed uniform Ni enrichment and graphite incorporation. Electrochemical and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) tests showed SASC castings had reduced corrosion rates and lower lead leaching, while machinability improved through the formation of short, granular chips instead of long, spiral chips. Compared with both the base alloy and Ni / Cu surface alloyed castings, SASC provided simultaneous improvements in corrosion resistance, lead leaching mitigation, and machinability. These findings demonstrate the potential of SASC technique for producing safer, high-performance brass components by integrating alloying and compositing in a single step.Introduction

[0265] Surface alloying modifies the surface of a base alloy by adding elements such as C, Ni, or Cr to improve wear, hardness, or corrosion resistance. It modifies surface composition and properties near the surface without altering the bulk casting, offering a cost-effective way to enhance performance by selectively alloying surface layers and reducing the need for expensive alloying elements. Surface-alloyed components are used in automotive, aerospace, tooling, and water industry applications. For brass components, surface alloying with Ni, Cr, and B using lasers has shown improvement in corrosion resistance; however, laser processing is costly and requires direct line-of-sight. Researchers have also explored diffusion coating, friction stir processing, and electron beam melting for surface alloying.

[0266] Surface alloying can be commercially valuable for brass used in water systems because it prolongs component life, reduces maintenance costs, and ensures compliance with water safety regulations. Early studies linked chloramine in water to accelerated impingement attack and cavitation; others showed that brass faucets lasted three times longer without chloramine exposure. Copper corrosion is strongly pH-dependent, with higher pH reducing chlorine-induced leaching. Later work suggested corrosion begins with oxidative attack by free chlorine, followed by dissolution of products, and is promoted by higher ionic strength, inorganic carbon, and temperature. Diffusion within oxide films slows overall corrosion. Alloying throughout the cross-section, as in Monel or red brass, show superior water-corrosion resistance compared with yellow brass.

[0267] A prominent corrosion mechanism in brass is dezincification, which involves the selective removal of Zn from the alloy surface exposed to the corrosive medium, resulting in a porous copper structure. This process occurs as Zn is more reactive than Cu and is more easily oxidized and dissolved in water, especially in the presence of slightly acidic or basic conditions. To prevent dezincification in brass alloys, additions of inhibitors like Arsenic (As) and Tin (Sn) have been used. Arsenic reduces Cu ions to form a protective cuprous oxide layer, while tin creates a film at grain boundaries to inhibit zinc diffusion. Using brass with lower Zn content or applying protective coatings can also help mitigate these corrosion processes. In chloride solutions at 68 F (20 C), α-brasses are prone to dezincification, particularly in stagnant areas and at elevated temperatures, even under flowing conditions. Dezincification is most severe in (α+β) and β-brasses. Brasses containing less than 30 wt % Zn predominantly form the α-phase and thus exhibit greater resistance to dezincification. Taps of red brasses and Monel alloys have shown much longer life than yellow brasses, suggesting that higher Ni and Cu contents reduce corrosion.

[0268] Leaching in brass alloys often involves the release of Pb and Cu into water, particularly in soft, corrosive conditions. Leaching is most pronounced during the first 24 hours of water stagnation, and regular flushing is an effective way to reduce metal concentrations. Adjusting the pH to around 7.5 or higher, maintaining sufficient alkalinity, and using orthophosphate as a corrosion inhibitor can further reduce lead and copper leaching by forming protective layers on the metal surfaces.

[0269] Lead has traditionally been added to brass to improve machinability by forming discrete particles that act as solid lubricants, resulting in smaller chips, smoother surface finish, and reduced tool wear. However, due to its toxicity and environmental impact, its use in pipes and fittings has been heavily restricted, and the U.S. Environmental Protection Agency (EPA) lowered the action level for lead in drinking water from 0.05 mg / L to 0.015 mg / L in 1991. These regulations have driven the development of lead-free brass alloys with acceptable machinability. Although lead decreases the corrosion rate of brass and reduces susceptibility to dezincification, shifting the breakdown potential to more noble values, its health risks outweigh these benefits. Lead levels in drinking water are closely monitored, and exceeding the 15-ppb action level under the EPA's Lead and Copper Rule requires corrective actions. In cases where no lead is added to copper alloys as an alloying element, there is residual Pb in alloys made from scrap, and this residual Pb can leach out when the cast components are in contact with water.

[0270] Bismuth, although not as toxic as lead, has been shown to be as effective as lead in improving machinability. This element is also non-soluble in brass alloys and has a relatively low melting point. However, the availability of Bi is limited, and its cost is much higher than that of Pb. Bi also segregates the grain boundaries, which causes an increase in the brittleness of the casting.

[0271] Incorporation of graphite in Cu alloy matrices has been reported in the literature using powder metallurgy techniques and, to a limited extent, using the stir casting technique. Graphite particles in Cu alloy matrix using a stir mixing process in the melt, where the graphite particles were intended to replace Pb for machinability purposes. In earlier work, graphite particles were incorporated throughout the cross-section of yellow brasses by stir mixing graphite and Ti in the entire melt, followed by casting. In these studies, the incorporation of graphite in the Cu alloys showed improvement in machinability, similar to the improvement in machinability achieved by additions of Pb. Additionally, the incorporation of graphite particles did not decrease the corrosion resistance of the Cu alloys. The present work improves upon prior work in that it eliminates the need to disperse graphite particles throughout the melt and throughout the castings, which is associated with nonuniform distribution of graphite in the melt and problems of graphite flotation in the melt and nonuniform distribution of graphite in slowly solidified castings. In the present work, these graphite particles are incorporated only near the surface, where they are intended to aid machining, reduce leaching, and improve corrosion resistance. The amount of graphite needed in SASC castings is significantly smaller compared to the case when graphite is incorporated throughout the cross-section of the castings.

[0272] The incorporation of graphite particles in copper alloys using powder metallurgy and stir casting have shown to improve wear resistance and machinability of copper alloys. However, powder metallurgy techniques are expensive and not suitable for producing plumbing components. Stir casting has been successfully used to incorporate graphite particles throughout the cross section of castings; the incorporation of graphite particles led to improvement in machinability of castings, similar to lead, improvement in wear resistance and has no measurable effect on corrosion rate. However, there were problems associated with achieving a uniform distribution of graphite in sand-cast copper alloy castings due to the flotation of particles.

[0273] Disclosed herein is a technique of surface alloying and surface compositing of copper alloy sand castings is described. The technique involves coating the molds or cores with slurry containing metal powders like Ni and Cu (for surface alloying) and Ni-coated graphite particles (for surface compositing). The casting surfaces in contact with the slurry when molten metal is poured into the mold are enriched in Ni and Cu (Surface Alloying), and in surface compositing, incorporate graphite particles near the surface when Ni-coated graphite particles are present in the slurry. The microstructure, chemical composition, and phases present in the surface alloyed and surface composited layers have been characterized, and improvements in corrosion resistance, machinability, and reduction of leaching of lead have been demonstrated. This technique represents an improvement over stir mixing and casting since graphite, Ni, and Cu are incorporated only near the surface, where they are needed for corrosion and leaching resistance and for machinability, thus reducing the amounts of Ni, Cu, and graphite needed in through-alloyed and through-composited castings. The surface alloying and surface compositing technique can be easily adopted for sand-cast copper alloy components.Materials and Methods

[0274] A total of eight sand cores were coated with slurries containing metal powders and Ni-Graphite powders at the University of Wisconsin-Milwaukee (UWM) and subsequently cast at a partner foundry. Each core was first coated with two layers of HA International Technikoat, a graphite-based mold and core wash designed to minimize reactions between molten metal and core sand, and then allowed to dry under ambient conditions for 24 hours. Following this, the cores were coated with a slurry containing Ni and Cu powders, graphite particles, and one of two water-based binders: polyvinyl alcohol (PVA) or a combination of PVA and a superplasticizer, in certain cases. Ni was incorporated specifically to improve the corrosion resistance and reduce leaching of the Bi-Alloy brass.

[0275] The slurry preparation process was a factor for achieving the desired surface alloying properties. C89836 brass (87-91 wt % Cu) was used as the base alloy, and Ni was selected as the alloying element to facilitate surface alloying. Incorporating Ni is expected to improve the corrosion resistance in the surface alloyed-surface composited (SASC) layer. The composition of the C89836 is shown in Table 2 and the composition of the slurries applied on the core surfaces is shown in Table 29 and Table 30.

[0276] The binder was prepared by dissolving the PVA powder in water at 176 F (80 C) to form a 10 wt % solution. The metal powders (Ni and Cu) and Ni-coated graphite particles were measured in quantities shown in Table 3, and the binder was added while maintaining a constant stirring rate. The viscosity of the slurry binder was important since low viscosity would lead to the separation of the powders. The slurry containing metal powders and Ni-coated graphite powders was applied on the surface of the cores to form a coating. The cores were then dried at room temperature for 48 hours, with no external heat applied during this process. The casting process has been schematically shown in FIG. 2, showing the application of the slurry on a sand core, followed by the pouring of the melt.TABLE 29Surface composite samples cast.SampleAlloyingGraphiteNoPowdersPowderBinder1-4Ni—CuNi-coatedPVA(1:1)Graphite5-8Ni—CuNi-coatedPVA + Superplasticizer(1:1)Graphite(SP)TABLE 30Composition of the Ni and Cu powders and Ni-coated graphiteparticles utilized to form the slurry for coating the coresSampleBinderNi-Graphite (g)Ni Powder (g)Cu Powder (g)Total Powder (g)1PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)2PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)3PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)4PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)5PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)6PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)7PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)8PVA + SP3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)9PVA3.168 (0.11 oz)5 (0.17 oz)5 (0.17 oz)13.168 (0.46 oz)Following casting in sand molds, the castings were sectioned from the surface alloyed-surface composited (SASC) regions for metallographic characterization. Samples were cut using a bandsaw, mounted in conductive phenolic resin, and ground sequentially with SiC abrasive papers of 180, 320, 600, 800, and 1200 grit. Final polishing was performed with 1 μm alumina suspension followed by 0.05 μm colloidal silica to obtain a mirror finish. Residual polishing media were removed using water and isopropyl alcohol. The polished samples were etched with Copper No. 2 (a ferric chloride-based etchant) to reveal the microstructure. Optical microscopy was conducted using a Nikon EPIPHOT 300 microscope under polarized light, while microstructural features were further examined with a JEOL 6460LV scanning electron microscope (SEM) using backscattered (BSE) and secondary electron (SE) imaging. Phase identification was conducted via X-ray diffraction (XRD) using a Bruker D8 Discover system was equipped with a Ni filter and Cu target and operated at 40 kV and 40 mA. The machinability test was performed using a sweeping tool with a depth profile of 0.635 mm ( 1 / 100th of an inch) on the samples to evaluate the chip formation behavior.

[0278] A potentiodynamic polarization test was performed to characterize the corrosion resistance of the samples. A potentiostat, SP-200 BioLogic, was used to run the corrosion test. The electrolyte used for the corrosion test was tap water, with an estimated chloramine concentration of ~2 ppm. The SASC samples and platinum wire mesh were used as the working electrodes and counter electrode, respectively, while Ag / AgCl was used as the reference electrode. The lead leaching tests were performed using a modified method of the NSF-61 testing method. As the samples only had one surface that was surface alloyed or surface composited, a borosilicate glass tube, open from both ends, was fixed on the surface alloyed and / or surface composited region using a binding medium. The tube was then filled with 30 ml of leaching liquid, which was tap water in this study, to initiate the test. As tap water contains chlorine or chloramine, the subsequent corrosion and leaching occurred from the sample surface. The test was conducted for a period of 24 hours at room temperature, following which the water in contact with surfaces was collected. The concentration of lead was quantified using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in the range of ppb. The base alloy, C89836, with a maximum lead concentration of 0.25 wt %, as well as a surface alloyed-surface composited sample (Ni—Cu-Graphite), were the samples tested in this study, along with two control samples of DI water and tap water.Results and Discussion

[0279] FIG. 26 shows the optical micrograph of a C89836 brass casting prepared using Ni—Cu powder and Ni-coated particles with a PVA binder in the slurry, which was coated on the cores. The micrographs show graphite particles that appear as dark particles dispersed in the surface layer. FIGS. 26(a) and 26(b) show that the SASC layer contains Ni-rich regions appearing as islands. FIGS. 26(c) and 26(d) show a higher-magnification view of the SASC layer, where the graphite particles appear as black particles surrounding the blue Ni-rich regions FIG. 26(d). FIGS. 26(e) and 26(f) show the Ni-enriched regions from the SASC layer, which appear as bright islands. FIGS. 26(e) and 26(f) highlight the Ni-enriched regions within the SASC layer. FIG. 26(f) shows these Ni rich regions or islands which sometimes contain dispersed Bi-enriched phases, since the C89839 alloy has bismuth.

[0280] The samples show successful formation of SASC layers of thicknesses ranging from 110 μm (≈0.00433 in) to 785 μm (≈0.0309 in). The microstructure shows enrichment in Ni and incorporation of graphite particles in the surface regions of the casting. The Ni coating present on the Ni-coated graphite particles and the Ni powder in the slurry coated on the cores led to an increase in the Ni wt % near the surface of the casting. In the surface alloyed and surface composited surface layer, the graphite particles are present around the Ni-rich islands, instead of being incorporated within the Ni-rich islands.

[0281] The presence of Ni coating on graphite particles presumably increased the wettability between the molten metal and the graphite particles and improved the adhesion between the graphite particles and the SASC layer. The SASC samples exhibited a high density of Ni-rich islands (approximately 41% area fraction), and they appear as numerous bright regions distributed throughout the layer (marked by white arrows in FIGS. 26(a) and 26(b)). When uncoated graphite powders were mixed in the slurry, there was no incorporation of graphite particles in the surface alloyed layer, demonstrating the critical role of Ni coating on the graphite particles for the incorporation of graphite particles in the surface layer of castings.

[0282] FIG. 27(a) shows the average thickness of the surface layers formed on C89836 brass substrate using Ni—Cu powders and Ni—Cu+Ni-Graphite powders in the slurry during the casting process. The surface alloyed and surface composited samples formed thinner layers when Ni—Cu+Ni-Graphite powders were incorporated in the slurry, measuring 315±35 μm (0.0124±0.0014 inches) with PVA and only 110±15 μm (0.0043±0.0006 inches) when PVA+Superplasticizer was used to form slurry (compared to the thickness of the surface alloyed layer from a prior study where only Ni and Cu powders were used in the metal slurry with PVA as the binding medium). The choice of binder in the slurry influences the thickness and percent coverage of the surface layer.

[0283] When Ni-coated graphite particles, with 58 wt % Ni and 42 wt % Graphite, were added to the slurry mixture, the area percentage of graphite particles in SASC layer was quantified. As seen in FIG. 3 (b), the SASC layer, formed when Ni—Cu+Ni-coated graphite particles were used with PVA binder to form the slurry, had the highest surface area coverage at 83±3%; process improvement will lead to 100% coverage of castings by surface alloy and SASC layer.

[0284] As shown in FIG. 28, when the slurry contains PVA+Superplasticizer as binder and Ni, Cu, and Ni-coated graphite powders in the slurry, about 26% area was occupied by graphite particles; under the same conditions, when PVA alone was used as a binder, only 17% area fraction was occupied by graphite particles. When Ni, Cu, and Ni coated graphite powders were present with both PVA and superplasticizer, a high fraction (approximately 41-42% area fraction) of the surface was occupied by Ni-rich islands (FIG. 29). It was observed in prior trials that when uncoated graphite particles were used in the slurry instead of Ni-coated graphite, no graphite was incorporated in the surface layer. Apparently, the Ni coating on graphite enhances the wetting with the melt and facilitates the incorporation of the powders in the slurry by the molten alloy.Compositional and Phase Analysis of SASC Layers

[0285] The elemental analysis of the SASC samples was performed to understand the composition of the phases formed during surface alloying and surface compositing. The increase in the wt % of Ni, alongside the incorporation of graphite particles, specifically in the surface layer, would result in a different microstructure compared to the base alloy or other Ni-rich alloys, such as Monel-400. The slurry composition consisted of pure Ni and Cu powders and Ni-coated graphite powders. The total quantity of Ni added to the system will be the sum of the Ni from the pure Ni powder and the Ni coating on the graphite particles. The purpose of this addition was to increase the Ni concentration of the surface layer, which would improve the corrosion resistance of the SASC layer. As discussed in the prior section, islands of Ni-rich phase were observed across the surface modified layer with the graphite particles present between these islands. The composition of typical Ni-rich islands is shown in FIG. 30(b), where spectrum 1 in the Ni-rich island has a Ni concentration of 46.58 wt %, which is significantly higher than the C89836 base alloy (~0.9 wt % Ni) as shown in FIG. 30. The average Ni concentration in the SASC layer was around 21.06 wt %, indicating successful enrichment of Ni in the SASC layer (compared to 0.9 wt % Nickel present in the base alloy).

[0286] FIG. 31 shows the elemental mapping of the SASC layer showing the distribution of Ni, Cu, C, and Zn. The composition of the SASC layer differs significantly from that of the base alloy. While the base is mainly Cu and Zn, the SASC layer shows a much higher concentration of Ni, and it also incorporates graphite particles. EDS map scans confirm the presence of the graphite particles, which are rich in carbon, and show Ni and Cu rich layers forming around the graphite particles.

[0287] The EDS composition scan in FIG. 32 and the EDS Elemental Dot Mapping in FIG. 33 of the SASC layers. FIG. 33 showed the presence of both Ni and Cu enriched regions which were surrounded by graphite particles. The EDS Line Scan in FIG. 34 shows an increase in the Ni and Cu concentrations around the periphery of the graphite particles. The Ni-rich zone surrounding the graphite particle was approximately 10 μm wide with the Cu concentration increasing to normal levels at a distance of 15 μm from the surface of the graphite particles.X-Ray Diffraction Pattern of the Base Alloy, SA Layer, and SASC Layer

[0288] In the case of yellow brass (60 / 40 Cu—Zn), the microstructure is composed of two phases, α and β phases. The α phase is rich in Cu, while the β phase is rich in Zn. The X-Ray Diffraction pattern of the base alloy shows the formation of a Cu—Ni—Zn phase as well as a Cu—Sn phase, which are expected on account of the composition of the base alloy which contains 4-7 wt % Sn and 2-4 wt % Zn. Bismuth, which was added to the melt for machinability, forms Bi particles during solidification, which are identified as the peak at 30°, shown in FIG. 35.

[0289] The X-Ray Diffraction pattern of the surface alloyed layer (formed when the Ni and Cu were included in the slurry) shows the formation of Ni-rich phases, which were not observed in the base C89836 alloy. As the slurry contained pure Ni and pure Cu powders, and the base alloy had 90% Copper and 0.9% Nickel, the surface alloyed layer contained a Ni—Cu solid solution phase. The X-Ray Diffraction pattern of the SASC layer showed the presence of Cu—Ni solid solution, Cu—Zn solid solution, and graphite particles.

[0290] The graphite particles were identified at a 2θ of 26.5°, confirming their presence. The Ni—Cu solid solution phase was visible as a smaller peak next to the Cu—Zn peak, but the same was not visible for the yellow brass or C89836 samples. C89836 has approximately 0.9 wt % of Ni, this amount is not enough for the formation of a significant amount of Ni—Cu phase. This changes on the addition of Ni powder as well as the Ni added through the Ni-coated graphite particles in the SASC layer. The localized increase of Ni concentration in the SASC layer leads to the formation of the Ni—Cu phase.Corrosion and Leaching Studies

[0291] A bar chart (FIG. 36) compares the average corrosion current (Icorr) for different surface-alloyed (SA) layer types, showing their relative resistance to corrosion. Since a higher Icorr corresponds to a higher corrosion rate (i.e., lower corrosion resistance), the comparison directly reflects material performance. Cu60Zn40 brass showed the highest Icorr (~1.3 μA), confirming its poor corrosion resistance. The base alloy, C89836, performed better (~0.70 μA), while Ni—Cu surface-alloyed castings further reduced Icorr to ~0.11 μA. The SASC layer, formed by incorporating Ni, Cu, and Ni-coated graphite, achieved the lowest values (0.05-0.13 μA). Among binder systems, PVA+Superplasticizer yielded the best performance (~0.05 μA). Small error bars confirmed the consistency of results. Overall, the castings with the SASC layer had the lowest corrosion rate, indicating that the SASC technique improves the corrosion resistance.

[0292] The galvanic potential difference between Monel and graphite is expected to be lower in tap water than in seawater. This reflects the environment-specific nature of the galvanic series: seawater, with its high conductivity and chloride content, amplifies potential separations and galvanic currents, while potable tap water has one to two orders of magnitude lower conductivity and far fewer aggressive ions, compressing potential differences and reducing galvanic driving forces. In chloraminated tap water (~2 ppm chloramine), the environment remains mildly oxidizing but less aggressive than aerated seawater. Under these conditions, Ni—Cu alloys with near-Monel compositions form stable passive films that shift their potentials to more noble values, while graphite remains near the oxygen reduction potential. The result is a reduced ΔE between near Monel composition and graphite in chloraminated potable water compared with seawater. The observed improvement in corrosion resistance of the graphite-Monel-brass composite is consistent with the reduction in galvanic potential differences in tap water relative to seawater, as well as the protective role of the Monel-like coating.

[0293] Lead leaching is another concern in brass alloys. Even when not deliberately added for machinability, residual lead can remain from recycled feedstock and subsequently leach into drinking water, where it poses serious health risks including birth defects and cancer. EPA regulations limit lead in drinking water to 15 ppb and restrict its addition in alloys to 0.25 wt %. Leaching tests were conducted over a 24-hour period at room temperature using an NSF-61 derived procedure. Controls with DI water and tap water established baseline concentrations and confirmed test reliability, as shown in FIG. 37.

[0294] Two as-cast samples, SASC and C89836, were tested in this study using a method that was derived from the NSF-61 test. The surface of the sample was exposed to a column of tap water, 30 ml in volume (≈1.8 in3), with a contact area of 1.77 cm2 (≈0.27 in2) at room temperature. Following the 24-hour period, the test liquid was analyzed using ICP-MS to quantify the lead concentration in parts per billion (ppb). It was observed that the water in contact with SASC layer, containing Ni, Cu, and Ni-graphite powders, did not have any lead leached into the water, whereas the base alloy, C89836, leached lead into the water, up to 1.43 ppb. The control sample of tap water had a lead concentration of 0.08 ppb, while in DI water, lead was not detected, showing the reliability of our testing technique. These preliminary tests indicate that surface alloyed and surface composited castings show reduced leaching of lead in water. It appears that the lead present in the base alloy does not contact the water due to the surface alloyed or SASC layer formed on the surface of the castings. The Ni-rich phase incorporating graphite particles reduces corrosion as well as leaching, in addition graphite is inert and will reduce any leaching in water.Machinability of Surface Alloyed and Surface Composited Layer

[0295] FIG. 38 compares chips collected during machining tests of four brass-based samples. A drill bit was swept across each surface at a cutting depth of 0.010 in (≈0.25 mm). Optical and SEM images are shown for 60-40 brass FIG. 38(a, a1), C89836 alloy FIG. 38(b, b1), Ni—Cu surface-alloyed layer FIG. 38(c, c1), and Ni-graphite SASC layer FIG. 38(d, d1). Higher-magnification SEM images FIG. 38(e, e1) include carbon mapping of the SASC chips, where green dashed circles highlight carbon-enriched regions. These confirm that embedded graphite particles promote chip breaking and thereby improve machinability. All images include a stereoscope millimeter scale bar (red, 1 mm (≈0.0394 in)) for reference.

[0296] Machining of 60-40 brass FIG. 38(a, a1) produced long, continuous ribbons, reflecting high ductility and poor chip breakage, making it difficult to machine. C89836 alloy FIG.38(b, b1) formed shorter, curled chips that were more fragmented, an effect attributed to bismuth additions that aid chip breakage. In contrast, the SASC layer FIG. 38(d, d1) produced the smallest and most granular chips, consisting of short segments and fine particles. This morphology indicates improved machinability due to the presence of graphite, which acts as a chip-breaking phase. Overall, chip size decreased progressively from 60-40 brass to C89836, to Ni—Cu SA, and finally to SASC, demonstrating a clear trend toward more fragmented, granular chips.

[0297] The results show that machinability improvements traditionally achieved by adding Pb or Bi can instead be realized through incorporation of Ni and graphite in a SASC layer. This provides a path to replace toxic alloying elements with a safer, surface-engineered alternative.

Examples

example embodiments

[0109]Embodiment 1: A low-cost method of producing a cast copper-based alloy component having an enriched, corrosion-resistant and wear-resistant surface, the method comprising:[0110](a) providing a copper-based alloy selected from the group consisting of yellow brass and red brass;[0111](b) preparing a slurry comprising:[0112]at least one powder selected from the group consisting of Cu, Ni, Cu—Ni, Cu—Sn, Al, Bi, Ni-coated graphite, Ni-coated Al2O3, and Ni-coated SiC; and[0113]a binder medium selected from the group consisting of water-based or alcohol-based binders, or superplasticizer;[0114](c) coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold; optionally repeating coating at least one of a sand core surface or a sand mold surface with the slurry to form a coated sand core or mold;[0115](d) heating the copper-based alloy to a temperature in the range of 1200° C. to 1300° C. or higher;[0116](e) pouring the molten c...

example 1

Surface Alloying and Surface Compositing of a Brass Alloy Castings Using Mold and Core Coatings

[0150]This work presents a low-cost casting process for surface alloyed surface compositing (SASC) of C89836 brass castings. Surfaces of the sand cores were coated with slurries containing varying amounts of Cu, Ni, and reinforcement particles, including Ni-coated Al2O3 and Ni-coated SiC powders, before pouring brass melts into the molds. In SASC samples, Al2O3 and SiC particles were concurrently incorporated into the casting surface, forming a surface composited region. Microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed the formation of a Ni-enriched surface and the successful incorporation of SiC or Al2O3 particles on the casting surface. Electrochemical testing indicated that SASC castings containing Al2O3 and SiC particles exhibited reduced corrosion rates compared to the base alloy. The SA and SASC ...

example 2

Factors Considered for Creating Alloyed and Composited Surface Layers on Brass

Introduction

Brass components in water distribution systems are particularly susceptible to corrosion when exposed to environments rich in chlorine and chloramines. This can lead to significant corrosion and early mechanical failure, imposing a substantial economic burden. This burden includes direct replacement costs, increased maintenance expenses, service interruptions, water loss from leaks, and potential public health risks from metal leaching.

The annual direct cost of corrosion in drinking water and sewer systems is estimated at $36 billion in the United States and the failure of brass components due to corrosion contributes significantly to this figure. The proposed surface alloying process significantly enhances the durability of brass components by targeting corrosion reduction at its surface. This process is practical and cost-effective, easily integrated into existing foundries without additional...

Claims

1. A method of making a copper alloy article, comprising:providing a slurry comprising:a surface modifying material comprising a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof, anda liquid binder;applying the slurry to an insulating tooling to form a slurry-coated tooling;contacting the slurry-coated tooling with molten copper alloy to form a surface modified layer disposed between the insulating tooling and the copper alloy; andsolidifying the molten copper alloy and surface modified layer.

2. The method of claim 1, wherein the surface modifying material comprises Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof.

3. The method of claim 1, wherein the metal-coated ceramic comprises Ni-coated SiC, Ni-coated Al2O3, or any combinations thereof, andwherein the metal-coated carbon-containing compound comprises Ni-coated graphite.

4. The method of claim 1, wherein the surface modifying material comprises particles.

5. The method of claim 4, wherein the surface modifying material comprises particles comprising at least one dimension ranging from about 5 μm to about 300 μm.

6. The method of claim 1, wherein the liquid binder comprises water, a polymer, or any combinations thereof.

7. The method of claim 6, wherein the polymer comprises polyvinyl alcohol.

8. The method of claim 6, wherein the liquid binder comprises about 0.5 wt % to about 30.0 wt % polymer, based on the total weight of the liquid binder.

9. The method of claim 6, wherein the liquid binder comprises a superplasticizer.

10. The method of claim 1, wherein the insulating tooling is a sand mold, a sand core, or any combination thereof.

11. The method of claim 1, wherein the molten copper alloy has a temperature above about 1200° C.

12. The method of claim 1, wherein the surface modifying material comprises Cu and Ni and, and wherein the ratio of Cu and Ni is about 1:1.

13. The method of claim 1, wherein applying the slurry to an insulating tooling further comprises drying the slurry.

14. The method of claim 1, wherein the steps of providing a slurry and applying the slurry to an insulating tooling to form a slurry-coated tooling are repeated two or more times to form a multi-layered slurry-coated tooling.

15. A corrosion-resistant article, comprising:a cast copper alloy component; anda surface modified layer disposed on a surface of the cast copper alloy component, the surface modified layer comprising a metal, a metallic alloy, a ceramic, a carbon-containing compound, a metal-coated ceramic, a metal-coated carbon-containing compound, or any combinations thereof.

16. The corrosion-resistant article of claim 15, wherein the surface modified layer comprises Cu, Ni, Sn, Al, Bi, Ni—Cu, Cu—Sn, Al2O3, SiC, graphite, metal-coated SiC, metal-coated graphite, or any combinations thereof.

17. The corrosion-resistant article of claim 15, wherein the surface modified layer is about 1 μm to about 5 mm thick.

18. The corrosion-resistant article of claim 15, wherein the cast copper alloy component is comprised of yellow brass, red brass, bronze, or any combinations thereof.

19. The corrosion-resistant article of claim 15, wherein the corrosion rate of the corrosion resistant article is reduced by 45% to 90%, as compared to the corrosion rate of the cast copper alloy component.

20. The corrosion-resistant article of claim 15, wherein the corrosion-resistance article comprises a reduced leach rate of one or more elements into water, as compared to the leach rate of one or more elements into water of the cast copper alloy component.

Images